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2021-08-11smp: Fix all kernel-doc warningsRandy Dunlap1-3/+11
Fix the following warnings: kernel/smp.c:1189: warning: cannot understand function prototype: 'struct smp_call_on_cpu_struct ' kernel/smp.c:788: warning: No description found for return value of 'smp_call_function_single_async' kernel/smp.c:990: warning: Function parameter or member 'wait' not described in 'smp_call_function_many' kernel/smp.c:990: warning: Excess function parameter 'flags' description in 'smp_call_function_many' kernel/smp.c:1198: warning: Function parameter or member 'work' not described in 'smp_call_on_cpu_struct' kernel/smp.c:1198: warning: Function parameter or member 'done' not described in 'smp_call_on_cpu_struct' kernel/smp.c:1198: warning: Function parameter or member 'func' not described in 'smp_call_on_cpu_struct' kernel/smp.c:1198: warning: Function parameter or member 'data' not described in 'smp_call_on_cpu_struct' kernel/smp.c:1198: warning: Function parameter or member 'ret' not described in 'smp_call_on_cpu_struct' kernel/smp.c:1198: warning: Function parameter or member 'cpu' not described in 'smp_call_on_cpu_struct' Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20210810225051.3938-1-rdunlap@infradead.org
2021-05-06smp: Fix smp_call_function_single_async prototypeArnd Bergmann1-13/+13
As of commit 966a967116e6 ("smp: Avoid using two cache lines for struct call_single_data"), the smp code prefers 32-byte aligned call_single_data objects for performance reasons, but the block layer includes an instance of this structure in the main 'struct request' that is more senstive to size than to performance here, see 4ccafe032005 ("block: unalign call_single_data in struct request"). The result is a violation of the calling conventions that clang correctly points out: block/blk-mq.c:630:39: warning: passing 8-byte aligned argument to 32-byte aligned parameter 2 of 'smp_call_function_single_async' may result in an unaligned pointer access [-Walign-mismatch] smp_call_function_single_async(cpu, &rq->csd); It does seem that the usage of the call_single_data without cache line alignment should still be allowed by the smp code, so just change the function prototype so it accepts both, but leave the default alignment unchanged for the other users. This seems better to me than adding a local hack to shut up an otherwise correct warning in the caller. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Jens Axboe <axboe@kernel.dk> Link: https://lkml.kernel.org/r/20210505211300.3174456-1-arnd@kernel.org
2021-03-06Merge branch 'locking/core' into x86/mm, to resolve conflictIngo Molnar1-11/+263
There's a non-trivial conflict between the parallel TLB flush framework and the IPI flush debugging code - merge them manually. Conflicts: kernel/smp.c Signed-off-by: Ingo Molnar <mingo@kernel.org>
2021-03-06smp: Micro-optimize smp_call_function_many_cond()Peter Zijlstra1-1/+1
Call the generic send_call_function_single_ipi() function, which will avoid the IPI when @last_cpu is idle. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2021-03-06smp: Inline on_each_cpu_cond() and on_each_cpu()Nadav Amit1-56/+0
Simplify the code and avoid having an additional function on the stack by inlining on_each_cpu_cond() and on_each_cpu(). Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Nadav Amit <namit@vmware.com> [ Minor edits. ] Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210220231712.2475218-10-namit@vmware.com
2021-03-06smp: Run functions concurrently in smp_call_function_many_cond()Nadav Amit1-68/+88
Currently, on_each_cpu() and similar functions do not exploit the potential of concurrency: the function is first executed remotely and only then it is executed locally. Functions such as TLB flush can take considerable time, so this provides an opportunity for performance optimization. To do so, modify smp_call_function_many_cond(), to allows the callers to provide a function that should be executed (remotely/locally), and run them concurrently. Keep other smp_call_function_many() semantic as it is today for backward compatibility: the called function is not executed in this case locally. smp_call_function_many_cond() does not use the optimized version for a single remote target that smp_call_function_single() implements. For synchronous function call, smp_call_function_single() keeps a call_single_data (which is used for synchronization) on the stack. Interestingly, it seems that not using this optimization provides greater performance improvements (greater speedup with a single remote target than with multiple ones). Presumably, holding data structures that are intended for synchronization on the stack can introduce overheads due to TLB misses and false-sharing when the stack is used for other purposes. Signed-off-by: Nadav Amit <namit@vmware.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com> Link: https://lore.kernel.org/r/20210220231712.2475218-2-namit@vmware.com
2021-03-06locking/csd_lock: Add more data to CSD lock debuggingJuergen Gross1-4/+222
In order to help identifying problems with IPI handling and remote function execution add some more data to IPI debugging code. There have been multiple reports of CPUs looping long times (many seconds) in smp_call_function_many() waiting for another CPU executing a function like tlb flushing. Most of these reports have been for cases where the kernel was running as a guest on top of KVM or Xen (there are rumours of that happening under VMWare, too, and even on bare metal). Finding the root cause hasn't been successful yet, even after more than 2 years of chasing this bug by different developers. Commit: 35feb60474bf4f7 ("kernel/smp: Provide CSD lock timeout diagnostics") tried to address this by adding some debug code and by issuing another IPI when a hang was detected. This helped mitigating the problem (the repeated IPI unlocks the hang), but the root cause is still unknown. Current available data suggests that either an IPI wasn't sent when it should have been, or that the IPI didn't result in the target CPU executing the queued function (due to the IPI not reaching the CPU, the IPI handler not being called, or the handler not seeing the queued request). Try to add more diagnostic data by introducing a global atomic counter which is being incremented when doing critical operations (before and after queueing a new request, when sending an IPI, and when dequeueing a request). The counter value is stored in percpu variables which can be printed out when a hang is detected. The data of the last event (consisting of sequence counter, source CPU, target CPU, and event type) is stored in a global variable. When a new event is to be traced, the data of the last event is stored in the event related percpu location and the global data is updated with the new event's data. This allows to track two events in one data location: one by the value of the event data (the event before the current one), and one by the location itself (the current event). A typical printout with a detected hang will look like this: csd: Detected non-responsive CSD lock (#1) on CPU#1, waiting 5000000003 ns for CPU#06 scf_handler_1+0x0/0x50(0xffffa2a881bb1410). csd: CSD lock (#1) handling prior scf_handler_1+0x0/0x50(0xffffa2a8813823c0) request. csd: cnt(00008cc): ffff->0000 dequeue (src cpu 0 == empty) csd: cnt(00008cd): ffff->0006 idle csd: cnt(0003668): 0001->0006 queue csd: cnt(0003669): 0001->0006 ipi csd: cnt(0003e0f): 0007->000a queue csd: cnt(0003e10): 0001->ffff ping csd: cnt(0003e71): 0003->0000 ping csd: cnt(0003e72): ffff->0006 gotipi csd: cnt(0003e73): ffff->0006 handle csd: cnt(0003e74): ffff->0006 dequeue (src cpu 0 == empty) csd: cnt(0003e7f): 0004->0006 ping csd: cnt(0003e80): 0001->ffff pinged csd: cnt(0003eb2): 0005->0001 noipi csd: cnt(0003eb3): 0001->0006 queue csd: cnt(0003eb4): 0001->0006 noipi csd: cnt now: 0003f00 The idea is to print only relevant entries. Those are all events which are associated with the hang (so sender side events for the source CPU of the hanging request, and receiver side events for the target CPU), and the related events just before those (for adding data needed to identify a possible race). Printing all available data would be possible, but this would add large amounts of data printed on larger configurations. Signed-off-by: Juergen Gross <jgross@suse.com> [ Minor readability edits. Breaks col80 but is far more readable. ] Signed-off-by: Ingo Molnar <mingo@kernel.org> Tested-by: Paul E. McKenney <paulmck@kernel.org> Link: https://lore.kernel.org/r/20210301101336.7797-4-jgross@suse.com
2021-03-06locking/csd_lock: Prepare more CSD lock debuggingJuergen Gross1-6/+10
In order to be able to easily add more CSD lock debugging data to struct call_function_data->csd move the call_single_data_t element into a sub-structure. Signed-off-by: Juergen Gross <jgross@suse.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210301101336.7797-3-jgross@suse.com
2021-03-06locking/csd_lock: Add boot parameter for controlling CSD lock debuggingJuergen Gross1-4/+34
Currently CSD lock debugging can be switched on and off via a kernel config option only. Unfortunately there is at least one problem with CSD lock handling pending for about 2 years now, which has been seen in different environments (mostly when running virtualized under KVM or Xen, at least once on bare metal). Multiple attempts to catch this issue have finally led to introduction of CSD lock debug code, but this code is not in use in most distros as it has some impact on performance. In order to be able to ship kernels with CONFIG_CSD_LOCK_WAIT_DEBUG enabled even for production use, add a boot parameter for switching the debug functionality on. This will reduce any performance impact of the debug coding to a bare minimum when not being used. Signed-off-by: Juergen Gross <jgross@suse.com> [ Minor edits. ] Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210301101336.7797-2-jgross@suse.com
2021-02-17smp: Process pending softirqs in flush_smp_call_function_from_idle()Sebastian Andrzej Siewior1-0/+4
send_call_function_single_ipi() may wake an idle CPU without sending an IPI. The woken up CPU will process the SMP-functions in flush_smp_call_function_from_idle(). Any raised softirq from within the SMP-function call will not be processed. Should the CPU have no tasks assigned, then it will go back to idle with pending softirqs and the NOHZ will rightfully complain. Process pending softirqs on return from flush_smp_call_function_queue(). Fixes: b2a02fc43a1f4 ("smp: Optimize send_call_function_single_ipi()") Reported-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20210123201027.3262800-2-bigeasy@linutronix.de
2020-11-27Merge branch 'linus' into sched/core, to resolve semantic conflictIngo Molnar1-1/+1
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2020-11-24smp: Cleanup smp_call_function*()Peter Zijlstra1-25/+25
Get rid of the __call_single_node union and cleanup the API a little to avoid external code relying on the structure layout as much. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
2020-10-19Merge tag 'core-rcu-2020-10-12' of ↵Linus Torvalds1-0/+134
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull RCU changes from Ingo Molnar: - Debugging for smp_call_function() - RT raw/non-raw lock ordering fixes - Strict grace periods for KASAN - New smp_call_function() torture test - Torture-test updates - Documentation updates - Miscellaneous fixes [ This doesn't actually pull the tag - I've dropped the last merge from the RCU branch due to questions about the series. - Linus ] * tag 'core-rcu-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (77 commits) smp: Make symbol 'csd_bug_count' static kernel/smp: Provide CSD lock timeout diagnostics smp: Add source and destination CPUs to __call_single_data rcu: Shrink each possible cpu krcp rcu/segcblist: Prevent useless GP start if no CBs to accelerate torture: Add gdb support rcutorture: Allow pointer leaks to test diagnostic code rcutorture: Hoist OOM registry up one level refperf: Avoid null pointer dereference when buf fails to allocate rcutorture: Properly synchronize with OOM notifier rcutorture: Properly set rcu_fwds for OOM handling torture: Add kvm.sh --help and update help message rcutorture: Add CONFIG_PROVE_RCU_LIST to TREE05 torture: Update initrd documentation rcutorture: Replace HTTP links with HTTPS ones locktorture: Make function torture_percpu_rwsem_init() static torture: document --allcpus argument added to the kvm.sh script rcutorture: Output number of elapsed grace periods rcutorture: Remove KCSAN stubs rcu: Remove unused "cpu" parameter from rcu_report_qs_rdp() ...
2020-10-16kernel/: fix repeated words in commentsRandy Dunlap1-1/+1
Fix multiple occurrences of duplicated words in kernel/. Fix one typo/spello on the same line as a duplicate word. Change one instance of "the the" to "that the". Otherwise just drop one of the repeated words. Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Link: https://lkml.kernel.org/r/98202fa6-8919-ef63-9efe-c0fad5ca7af1@infradead.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-09-04smp: Make symbol 'csd_bug_count' staticWei Yongjun1-1/+1
The sparse tool complains as follows: kernel/smp.c:107:10: warning: symbol 'csd_bug_count' was not declared. Should it be static? Because variable is not used outside of smp.c, this commit marks it static. Reported-by: Hulk Robot <hulkci@huawei.com> Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
2020-09-04kernel/smp: Provide CSD lock timeout diagnosticsPaul E. McKenney1-2/+130
This commit causes csd_lock_wait() to emit diagnostics when a CPU fails to respond quickly enough to one of the smp_call_function() family of function calls. These diagnostics are enabled by a new CSD_LOCK_WAIT_DEBUG Kconfig option that depends on DEBUG_KERNEL. This commit was inspired by an earlier patch by Josef Bacik. [ paulmck: Fix for syzbot+0f719294463916a3fc0e@syzkaller.appspotmail.com ] [ paulmck: Fix KASAN use-after-free issue reported by Qian Cai. ] [ paulmck: Fix botched nr_cpu_ids comparison per Dan Carpenter. ] [ paulmck: Apply Peter Zijlstra feedback. ] Link: https://lore.kernel.org/lkml/00000000000042f21905a991ecea@google.com Link: https://lore.kernel.org/lkml/0000000000002ef21705a9933cf3@google.com Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-09-04smp: Add source and destination CPUs to __call_single_dataPaul E. McKenney1-0/+6
This commit adds a destination CPU to __call_single_data, and is inspired by an earlier commit by Peter Zijlstra. This version adds #ifdef to permit use by 32-bit systems and supplying the destination CPU for all smp_call_function*() requests, not just smp_call_function_single(). If need be, 32-bit systems could be accommodated by shrinking the flags field to 16 bits (the atomic_t variant is currently unused) and by providing only eight bits for CPU on such systems. It is not clear that the addition of the fields to __call_single_node are really needed. [ paulmck: Apply Boqun Feng feedback on 32-bit builds. ] Link: https://lore.kernel.org/lkml/20200615164048.GC2531@hirez.programming.kicks-ass.net/ Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
2020-07-22smp: Fix a potential usage of stale nr_cpusMuchun Song1-2/+1
The get_option() maybe return 0, it means that the nr_cpus is not initialized. Then we will use the stale nr_cpus to initialize the nr_cpu_ids. So fix it. Signed-off-by: Muchun Song <songmuchun@bytedance.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200716070457.53255-1-songmuchun@bytedance.com
2020-06-28smp, irq_work: Continue smp_call_function*() and irq_work*() integrationPeter Zijlstra1-18/+0
Instead of relying on BUG_ON() to ensure the various data structures line up, use a bunch of horrible unions to make it all automatic. Much of the union magic is to ensure irq_work and smp_call_function do not (yet) see the members of their respective data structures change name. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lkml.kernel.org/r/20200622100825.844455025@infradead.org
2020-06-03Merge tag 'sched-core-2020-06-02' of ↵Linus Torvalds1-43/+132
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler updates from Ingo Molnar: "The changes in this cycle are: - Optimize the task wakeup CPU selection logic, to improve scalability and reduce wakeup latency spikes - PELT enhancements - CFS bandwidth handling fixes - Optimize the wakeup path by remove rq->wake_list and replacing it with ->ttwu_pending - Optimize IPI cross-calls by making flush_smp_call_function_queue() process sync callbacks first. - Misc fixes and enhancements" * tag 'sched-core-2020-06-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (36 commits) irq_work: Define irq_work_single() on !CONFIG_IRQ_WORK too sched/headers: Split out open-coded prototypes into kernel/sched/smp.h sched: Replace rq::wake_list sched: Add rq::ttwu_pending irq_work, smp: Allow irq_work on call_single_queue smp: Optimize send_call_function_single_ipi() smp: Move irq_work_run() out of flush_smp_call_function_queue() smp: Optimize flush_smp_call_function_queue() sched: Fix smp_call_function_single_async() usage for ILB sched/core: Offload wakee task activation if it the wakee is descheduling sched/core: Optimize ttwu() spinning on p->on_cpu sched: Defend cfs and rt bandwidth quota against overflow sched/cpuacct: Fix charge cpuacct.usage_sys sched/fair: Replace zero-length array with flexible-array sched/pelt: Sync util/runnable_sum with PELT window when propagating sched/cpuacct: Use __this_cpu_add() instead of this_cpu_ptr() sched/fair: Optimize enqueue_task_fair() sched: Make scheduler_ipi inline sched: Clean up scheduler_ipi() sched/core: Simplify sched_init() ...
2020-06-02irq_work: Define irq_work_single() on !CONFIG_IRQ_WORK tooIngo Molnar1-2/+0
Some SMP platforms don't have CONFIG_IRQ_WORK defined, resulting in a link error at build time. Define a stub and clean up the prototype definitions. Reported-by: kbuild test robot <lkp@intel.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2020-05-28sched/headers: Split out open-coded prototypes into kernel/sched/smp.hIngo Molnar1-4/+1
Move the prototypes for sched_ttwu_pending() and send_call_function_single_ipi() into the newly created kernel/sched/smp.h header, to make sure they are all the same, and to architectures happy that use -Wmissing-prototypes. Signed-off-by: Ingo Molnar <mingo@kernel.org>
2020-05-28sched: Replace rq::wake_listPeter Zijlstra1-7/+40
The recent commit: 90b5363acd47 ("sched: Clean up scheduler_ipi()") got smp_call_function_single_async() subtly wrong. Even though it will return -EBUSY when trying to re-use a csd, that condition is not atomic and still requires external serialization. The change in ttwu_queue_remote() got this wrong. While on first reading ttwu_queue_remote() has an atomic test-and-set that appears to serialize the use, the matching 'release' is not in the right place to actually guarantee this serialization. The actual race is vs the sched_ttwu_pending() call in the idle loop; that can run the wakeup-list without consuming the CSD. Instead of trying to chain the lists, merge them. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20200526161908.129371594@infradead.org
2020-05-28irq_work, smp: Allow irq_work on call_single_queuePeter Zijlstra1-46/+73
Currently irq_work_queue_on() will issue an unconditional arch_send_call_function_single_ipi() and has the handler do irq_work_run(). This is unfortunate in that it makes the IPI handler look at a second cacheline and it misses the opportunity to avoid the IPI. Instead note that struct irq_work and struct __call_single_data are very similar in layout, so use a few bits in the flags word to encode a type and stick the irq_work on the call_single_queue list. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20200526161908.011635912@infradead.org
2020-05-28smp: Optimize send_call_function_single_ipi()Peter Zijlstra1-1/+15
Just like the ttwu_queue_remote() IPI, make use of _TIF_POLLING_NRFLAG to avoid sending IPIs to idle CPUs. [ mingo: Fix UP build bug. ] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20200526161907.953304789@infradead.org
2020-05-28smp: Move irq_work_run() out of flush_smp_call_function_queue()Peter Zijlstra1-8/+9
This ensures flush_smp_call_function_queue() is strictly about call_single_queue. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20200526161907.895109676@infradead.org
2020-05-28smp: Optimize flush_smp_call_function_queue()Peter Zijlstra1-4/+23
The call_single_queue can contain (two) different callbacks, synchronous and asynchronous. The current interrupt handler runs them in-order, which means that remote CPUs that are waiting for their synchronous call can be delayed by running asynchronous callbacks. Rework the interrupt handler to first run the synchonous callbacks. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20200526161907.836818381@infradead.org
2020-04-19smp: Use smp_call_func_t in on_each_cpu()Kaitao Cheng1-1/+1
Use smp_call_func_t instead of the open coded function pointer argument. Signed-off-by: Kaitao Cheng <pilgrimtao@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://lkml.kernel.org/r/20200417162451.91969-1-pilgrimtao@gmail.com
2020-03-25cpu/hotplug: Move bringup of secondary CPUs out of smp_init()Qais Yousef1-8/+1
This is the last direct user of cpu_up() before it can become an internal implementation detail of the cpu subsystem. Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20200323135110.30522-17-qais.yousef@arm.com
2020-03-06smp: Allow smp_call_function_single_async() to insert locked csdPeter Xu1-3/+11
Previously we will raise an warning if we want to insert a csd object which is with the LOCK flag set, and if it happens we'll also wait for the lock to be released. However, this operation does not match perfectly with how the function is named - the name with "_async" suffix hints that this function should not block, while we will. This patch changed this behavior by simply return -EBUSY instead of waiting, at the meantime we allow this operation to happen without warning the user to change this into a feature when the caller wants to "insert a csd object, if it's there, just wait for that one". This is pretty safe because in flush_smp_call_function_queue() for async csd objects (where csd->flags&SYNC is zero) we'll first do the unlock then we call the csd->func(). So if we see the csd->flags&LOCK is true in smp_call_function_single_async(), then it's guaranteed that csd->func() will be called after this smp_call_function_single_async() returns -EBUSY. Update the comment of the function too to refect this. Signed-off-by: Peter Xu <peterx@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20191216213125.9536-2-peterx@redhat.com
2020-01-28smp: Remove superfluous cond_func check in smp_call_function_many_cond()Sebastian Andrzej Siewior1-1/+1
It was requested to remove the cond_func check but the follow up patch was overlooked. Remove it now. Fixes: 67719ef25eeb ("smp: Add a smp_cond_func_t argument to smp_call_function_many()") Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20200127083915.434tdkztorkklpdu@linutronix.de
2020-01-24smp: Remove allocation mask from on_each_cpu_cond.*()Sebastian Andrzej Siewior1-10/+3
The allocation mask is no longer used by on_each_cpu_cond() and on_each_cpu_cond_mask() and can be removed. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20200117090137.1205765-4-bigeasy@linutronix.de
2020-01-24smp: Add a smp_cond_func_t argument to smp_call_function_many()Sebastian Andrzej Siewior1-43/+38
on_each_cpu_cond_mask() allocates a new CPU mask. The newly allocated mask is a subset of the provided mask based on the conditional function. This memory allocation can be avoided by extending smp_call_function_many() with the conditional function and performing the remote function call based on the mask and the conditional function. Rename smp_call_function_many() to smp_call_function_many_cond() and add the smp_cond_func_t argument. If smp_cond_func_t is provided then it is used before invoking the function. Provide smp_call_function_many() with cond_func set to NULL. Let on_each_cpu_cond_mask() use smp_call_function_many_cond(). Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20200117090137.1205765-3-bigeasy@linutronix.de
2020-01-24smp: Use smp_cond_func_t as type for the conditional functionSebastian Andrzej Siewior1-6/+5
Use a typdef for the conditional function instead defining it each time in the function prototype. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20200117090137.1205765-2-bigeasy@linutronix.de
2019-07-20smp: Warn on function calls from softirq contextPeter Zijlstra1-0/+16
It's clearly documented that smp function calls cannot be invoked from softirq handling context. Unfortunately nothing enforces that or emits a warning. A single function call can be invoked from softirq context only via smp_call_function_single_async(). The only legit context is task context, so add a warning to that effect. Reported-by: luferry <luferry@163.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20190718160601.GP3402@hirez.programming.kicks-ass.net
2019-06-23smp: Remove smp_call_function() and on_each_cpu() return valuesNadav Amit1-7/+3
The return value is fixed. Remove it and amend the callers. [ tglx: Fixup arm/bL_switcher and powerpc/rtas ] Signed-off-by: Nadav Amit <namit@vmware.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Richard Henderson <rth@twiddle.net> Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Cc: Matt Turner <mattst88@gmail.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> Link: https://lkml.kernel.org/r/20190613064813.8102-2-namit@vmware.com
2019-06-23smp: Do not mark call_function_data as sharedNadav Amit1-1/+1
cfd_data is marked as shared, but although it hold pointers to shared data structures, it is private per core. Signed-off-by: Nadav Amit <namit@vmware.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Rik van Riel <riel@surriel.com> Link: https://lkml.kernel.org/r/20190613064813.8102-8-namit@vmware.com
2019-05-21treewide: Add SPDX license identifier for missed filesThomas Gleixner1-0/+1
Add SPDX license identifiers to all files which: - Have no license information of any form - Have EXPORT_.*_SYMBOL_GPL inside which was used in the initial scan/conversion to ignore the file These files fall under the project license, GPL v2 only. The resulting SPDX license identifier is: GPL-2.0-only Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-01-30cpu/hotplug: Fix "SMT disabled by BIOS" detection for KVMJosh Poimboeuf1-2/+0
With the following commit: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS") ... the hotplug code attempted to detect when SMT was disabled by BIOS, in which case it reported SMT as permanently disabled. However, that code broke a virt hotplug scenario, where the guest is booted with only primary CPU threads, and a sibling is brought online later. The problem is that there doesn't seem to be a way to reliably distinguish between the HW "SMT disabled by BIOS" case and the virt "sibling not yet brought online" case. So the above-mentioned commit was a bit misguided, as it permanently disabled SMT for both cases, preventing future virt sibling hotplugs. Going back and reviewing the original problems which were attempted to be solved by that commit, when SMT was disabled in BIOS: 1) /sys/devices/system/cpu/smt/control showed "on" instead of "notsupported"; and 2) vmx_vm_init() was incorrectly showing the L1TF_MSG_SMT warning. I'd propose that we instead consider #1 above to not actually be a problem. Because, at least in the virt case, it's possible that SMT wasn't disabled by BIOS and a sibling thread could be brought online later. So it makes sense to just always default the smt control to "on" to allow for that possibility (assuming cpuid indicates that the CPU supports SMT). The real problem is #2, which has a simple fix: change vmx_vm_init() to query the actual current SMT state -- i.e., whether any siblings are currently online -- instead of looking at the SMT "control" sysfs value. So fix it by: a) reverting the original "fix" and its followup fix: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS") bc2d8d262cba ("cpu/hotplug: Fix SMT supported evaluation") and b) changing vmx_vm_init() to query the actual current SMT state -- instead of the sysfs control value -- to determine whether the L1TF warning is needed. This also requires the 'sched_smt_present' variable to exported, instead of 'cpu_smt_control'. Fixes: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS") Reported-by: Igor Mammedov <imammedo@redhat.com> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Joe Mario <jmario@redhat.com> Cc: Jiri Kosina <jikos@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: kvm@vger.kernel.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/e3a85d585da28cc333ecbc1e78ee9216e6da9396.1548794349.git.jpoimboe@redhat.com
2018-10-09smp,cpumask: introduce on_each_cpu_cond_maskRik van Riel1-4/+13
Introduce a variant of on_each_cpu_cond that iterates only over the CPUs in a cpumask, in order to avoid making callbacks for every single CPU in the system when we only need to test a subset. Cc: npiggin@gmail.com Cc: mingo@kernel.org Cc: will.deacon@arm.com Cc: songliubraving@fb.com Cc: kernel-team@fb.com Cc: hpa@zytor.com Cc: luto@kernel.org Signed-off-by: Rik van Riel <riel@surriel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: http://lkml.kernel.org/r/20180926035844.1420-5-riel@surriel.com
2018-10-09smp: use __cpumask_set_cpu in on_each_cpu_condRik van Riel1-1/+1
The code in on_each_cpu_cond sets CPUs in a locally allocated bitmask, which should never be used by other CPUs simultaneously. There is no need to use locked memory accesses to set the bits in this bitmap. Switch to __cpumask_set_cpu. Cc: npiggin@gmail.com Cc: mingo@kernel.org Cc: will.deacon@arm.com Cc: songliubraving@fb.com Cc: kernel-team@fb.com Cc: hpa@zytor.com Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Rik van Riel <riel@surriel.com> Reviewed-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: http://lkml.kernel.org/r/20180926035844.1420-4-riel@surriel.com
2018-08-07cpu/hotplug: Fix SMT supported evaluationThomas Gleixner1-0/+2
Josh reported that the late SMT evaluation in cpu_smt_state_init() sets cpu_smt_control to CPU_SMT_NOT_SUPPORTED in case that 'nosmt' was supplied on the kernel command line as it cannot differentiate between SMT disabled by BIOS and SMT soft disable via 'nosmt'. That wreckages the state and makes the sysfs interface unusable. Rework this so that during bringup of the non boot CPUs the availability of SMT is determined in cpu_smt_allowed(). If a newly booted CPU is not a 'primary' thread then set the local cpu_smt_available marker and evaluate this explicitely right after the initial SMP bringup has finished. SMT evaulation on x86 is a trainwreck as the firmware has all the information _before_ booting the kernel, but there is no interface to query it. Fixes: 73d5e2b47264 ("cpu/hotplug: detect SMT disabled by BIOS") Reported-by: Josh Poimboeuf <jpoimboe@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2017-11-08smp/core: Use lockdep to assert IRQs are disabled/enabledFrederic Weisbecker1-1/+1
Use lockdep to check that IRQs are enabled or disabled as expected. This way the sanity check only shows overhead when concurrency correctness debug code is enabled. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: David S . Miller <davem@davemloft.net> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tejun Heo <tj@kernel.org> Link: http://lkml.kernel.org/r/1509980490-4285-7-git-send-email-frederic@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-09treewide: make "nr_cpu_ids" unsignedAlexey Dobriyan1-1/+1
First, number of CPUs can't be negative number. Second, different signnnedness leads to suboptimal code in the following cases: 1) kmalloc(nr_cpu_ids * sizeof(X)); "int" has to be sign extended to size_t. 2) while (loff_t *pos < nr_cpu_ids) MOVSXD is 1 byte longed than the same MOV. Other cases exist as well. Basically compiler is told that nr_cpu_ids can't be negative which can't be deduced if it is "int". Code savings on allyesconfig kernel: -3KB add/remove: 0/0 grow/shrink: 25/264 up/down: 261/-3631 (-3370) function old new delta coretemp_cpu_online 450 512 +62 rcu_init_one 1234 1272 +38 pci_device_probe 374 399 +25 ... pgdat_reclaimable_pages 628 556 -72 select_fallback_rq 446 369 -77 task_numa_find_cpu 1923 1807 -116 Link: http://lkml.kernel.org/r/20170819114959.GA30580@avx2 Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-08-29smp: Avoid using two cache lines for struct call_single_dataYing Huang1-15/+17
struct call_single_data is used in IPIs to transfer information between CPUs. Its size is bigger than sizeof(unsigned long) and less than cache line size. Currently it is not allocated with any explicit alignment requirements. This makes it possible for allocated call_single_data to cross two cache lines, which results in double the number of the cache lines that need to be transferred among CPUs. This can be fixed by requiring call_single_data to be aligned with the size of call_single_data. Currently the size of call_single_data is the power of 2. If we add new fields to call_single_data, we may need to add padding to make sure the size of new definition is the power of 2 as well. Fortunately, this is enforced by GCC, which will report bad sizes. To set alignment requirements of call_single_data to the size of call_single_data, a struct definition and a typedef is used. To test the effect of the patch, I used the vm-scalability multiple thread swap test case (swap-w-seq-mt). The test will create multiple threads and each thread will eat memory until all RAM and part of swap is used, so that huge number of IPIs are triggered when unmapping memory. In the test, the throughput of memory writing improves ~5% compared with misaligned call_single_data, because of faster IPIs. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Huang, Ying <ying.huang@intel.com> [ Add call_single_data_t and align with size of call_single_data. ] Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Aaron Lu <aaron.lu@intel.com> Cc: Borislav Petkov <bp@suse.de> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Juergen Gross <jgross@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/87bmnqd6lz.fsf@yhuang-mobile.sh.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-05-23smp, cpumask: Use non-atomic cpumask_{set,clear}_cpu()Peter Zijlstra1-2/+2
The cpumasks in smp_call_function_many() are private and not subject to concurrency, atomic bitops are pointless and expensive. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-05-23smp: Avoid sending needless IPI in smp_call_function_many()Aaron Lu1-2/+12
Inter-Processor-Interrupt(IPI) is needed when a page is unmapped and the process' mm_cpumask() shows the process has ever run on other CPUs. page migration, page reclaim all need IPIs. The number of IPI needed to send to different CPUs is especially large for multi-threaded workload since mm_cpumask() is per process. For smp_call_function_many(), whenever a CPU queues a CSD to a target CPU, it will send an IPI to let the target CPU to handle the work. This isn't necessary - we need only send IPI when queueing a CSD to an empty call_single_queue. The reason: flush_smp_call_function_queue() that is called upon a CPU receiving an IPI will empty the queue and then handle all of the CSDs there. So if the target CPU's call_single_queue is not empty, we know that: i. An IPI for the target CPU has already been sent by 'previous queuers'; ii. flush_smp_call_function_queue() hasn't emptied that CPU's queue yet. Thus, it's safe for us to just queue our CSD there without sending an addtional IPI. And for the 'previous queuers', we can limit it to the first queuer. To demonstrate the effect of this patch, a multi-thread workload that spawns 80 threads to equally consume 100G memory is used. This is tested on a 2 node broadwell-EP which has 44cores/88threads and 32G memory. So after 32G memory is used up, page reclaiming starts to happen a lot. With this patch, IPI number dropped 88% and throughput increased about 15% for the above workload. Signed-off-by: Aaron Lu <aaron.lu@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tim Chen <tim.c.chen@linux.intel.com> Link: http://lkml.kernel.org/r/20170519075331.GE2084@aaronlu.sh.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-03-02sched/headers: Prepare for new header dependencies before moving code to ↵Ingo Molnar1-0/+1
<linux/sched/idle.h> We are going to split <linux/sched/idle.h> out of <linux/sched.h>, which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder <linux/sched/idle.h> file that just maps to <linux/sched.h> to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2016-10-26kernel/smp: Tell the user we're bringing up secondary CPUsMichael Ellerman1-0/+2
Currently we don't print anything before starting to bring up secondary CPUs. This can be confusing if it takes a long time to bring up the secondaries, or if the kernel crashes while doing so and produces no further output. On x86 they work around this by detecting when the first secondary CPU comes up and printing a message (see announce_cpu()). But doing it in smp_init() is simpler and works for all arches. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Reviewed-by: Borislav Petkov <bp@suse.de> Cc: akpm@osdl.org Cc: jgross@suse.com Cc: ak@linux.intel.com Cc: tim.c.chen@linux.intel.com Cc: len.brown@intel.com Cc: peterz@infradead.org Cc: richard@nod.at Cc: jolsa@redhat.com Cc: boris.ostrovsky@oracle.com Cc: mgorman@techsingularity.net Link: http://lkml.kernel.org/r/1477460275-8266-3-git-send-email-mpe@ellerman.id.au Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2016-10-26kernel/smp: Make the SMP boot message common on all archesMichael Ellerman1-6/+7
Currently after bringing up secondary CPUs all arches print "Brought up %d CPUs". On x86 they also print the number of nodes that were brought online. It would be nice to also print the number of nodes on other arches. Although we could override smp_announce() on the other ~10 NUMA aware arches, it seems simpler to just always print the number of nodes. On non-NUMA arches there is just always 1 node. Having done that, smp_announce() is no longer weak, and seems small enough to just pull directly into smp_init(). Also update the printing of "%d CPUs" to be smart when an SMP kernel is booted on a single CPU system, or when only one CPU is available, eg: smp: Brought up 2 nodes, 1 CPU Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Reviewed-by: Borislav Petkov <bp@suse.de> Cc: akpm@osdl.org Cc: jgross@suse.com Cc: ak@linux.intel.com Cc: tim.c.chen@linux.intel.com Cc: len.brown@intel.com Cc: peterz@infradead.org Cc: richard@nod.at Cc: jolsa@redhat.com Cc: boris.ostrovsky@oracle.com Cc: mgorman@techsingularity.net Link: http://lkml.kernel.org/r/1477460275-8266-2-git-send-email-mpe@ellerman.id.au Signed-off-by: Thomas Gleixner <tglx@linutronix.de>