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2013-05-31vtime: Use consistent clocks among nohz accountingFrederic Weisbecker1-2/+2
While computing the cputime delta of dynticks CPUs, we are mixing up clocks of differents natures: * local_clock() which takes care of unstable clock sources and fix these if needed. * sched_clock() which is the weaker version of local_clock(). It doesn't compute any fixup in case of unstable source. If the clock source is stable, those two clocks are the same and we can safely compute the difference against two random points. Otherwise it results in random deltas as sched_clock() can randomly drift away, back or forward, from local_clock(). As a consequence, some strange behaviour with unstable tsc has been observed such as non progressing constant zero cputime. (The 'top' command showing no load). Fix this by only using local_clock(), or its irq safe/remote equivalent, in vtime code. Reported-by: Mike Galbraith <efault@gmx.de> Suggested-by: Mike Galbraith <efault@gmx.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-01-27cputime: Safely read cputime of full dynticks CPUsFrederic Weisbecker1-24/+23
While remotely reading the cputime of a task running in a full dynticks CPU, the values stored in utime/stime fields of struct task_struct may be stale. Its values may be those of the last kernel <-> user transition time snapshot and we need to add the tickless time spent since this snapshot. To fix this, flush the cputime of the dynticks CPUs on kernel <-> user transition and record the time / context where we did this. Then on top of this snapshot and the current time, perform the fixup on the reader side from task_times() accessors. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Namhyung Kim <namhyung.kim@lge.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> [fixed kvm module related build errors] Signed-off-by: Sedat Dilek <sedat.dilek@gmail.com>
2013-01-27kvm: Prepare to add generic guest entry/exit callbacksFrederic Weisbecker1-2/+0
Do some ground preparatory work before adding guest_enter() and guest_exit() context tracking callbacks. Those will be later used to read the guest cputime safely when we run in full dynticks mode. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Gleb Natapov <gleb@redhat.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Namhyung Kim <namhyung.kim@lge.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
2013-01-27cputime: Allow dynamic switch between tick/virtual based cputime accountingFrederic Weisbecker1-0/+8
Allow to dynamically switch between tick and virtual based cputime accounting. This way we can provide a kind of "on-demand" virtual based cputime accounting. In this mode, the kernel relies on the context tracking subsystem to dynamically probe on kernel boundaries. This is in preparation for being able to stop the timer tick in more places than just the idle state. Doing so will depend on CONFIG_VIRT_CPU_ACCOUNTING_GEN which makes it possible to account the cputime without the tick by hooking on kernel/user boundaries. Depending whether the tick is stopped or not, we can switch between tick and vtime based accounting anytime in order to minimize the overhead associated to user hooks. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Namhyung Kim <namhyung.kim@lge.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
2013-01-27cputime: Generic on-demand virtual cputime accountingFrederic Weisbecker1-0/+16
If we want to stop the tick further idle, we need to be able to account the cputime without using the tick. Virtual based cputime accounting solves that problem by hooking into kernel/user boundaries. However implementing CONFIG_VIRT_CPU_ACCOUNTING require low level hooks and involves more overhead. But we already have a generic context tracking subsystem that is required for RCU needs by archs which plan to shut down the tick outside idle. This patch implements a generic virtual based cputime accounting that relies on these generic kernel/user hooks. There are some upsides of doing this: - This requires no arch code to implement CONFIG_VIRT_CPU_ACCOUNTING if context tracking is already built (already necessary for RCU in full tickless mode). - We can rely on the generic context tracking subsystem to dynamically (de)activate the hooks, so that we can switch anytime between virtual and tick based accounting. This way we don't have the overhead of the virtual accounting when the tick is running periodically. And one downside: - There is probably more overhead than a native virtual based cputime accounting. But this relies on hooks that are already set anyway. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Namhyung Kim <namhyung.kim@lge.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
2012-11-19vtime: Explicitly account pending user time on process tickFrederic Weisbecker1-0/+1
All vtime implementations just flush the user time on process tick. Consolidate that in generic code by calling a user time accounting helper. This avoids an indirect call in ia64 and prepare to also consolidate vtime context switch code. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
2012-11-19vtime: Remove the underscore prefix invasionFrederic Weisbecker1-4/+4
Prepending irq-unsafe vtime APIs with underscores was actually a bad idea as the result is a big mess in the API namespace that is even waiting to be further extended. Also these helpers are always called from irq safe callers except kvm. Just provide a vtime_account_system_irqsafe() for this specific case so that we can remove the underscore prefix on other vtime functions. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
2012-10-30cputime: Separate irqtime accounting from generic vtimeFrederic Weisbecker1-10/+8
vtime_account() doesn't have the same role in CONFIG_VIRT_CPU_ACCOUNTING and CONFIG_IRQ_TIME_ACCOUNTING. In the first case it handles time accounting in any context. In the second case it only handles irq time accounting. So when vtime_account() is called from outside vtime_account_irq_*() this call is pointless to CONFIG_IRQ_TIME_ACCOUNTING. To fix the confusion, change vtime_account() to irqtime_account_irq() in CONFIG_IRQ_TIME_ACCOUNTING. This way we ensure future account_vtime() calls won't waste useless cycles in the irqtime APIs. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
2012-10-30cputime: Specialize irq vtime hooksFrederic Weisbecker1-0/+25
With CONFIG_VIRT_CPU_ACCOUNTING, when vtime_account() is called in irq entry/exit, we perform a check on the context: if we are interrupting the idle task we account the pending cputime to idle, otherwise account to system time or its sub-areas: tsk->stime, hardirq time, softirq time, ... However this check for idle only concerns the hardirq entry and softirq entry: * Hardirq may directly interrupt the idle task, in which case we need to flush the pending CPU time to idle. * The idle task may be directly interrupted by a softirq if it calls local_bh_enable(). There is probably no such call in any idle task but we need to cover every case. Ksoftirqd is not concerned because the idle time is flushed on context switch and softirq in the end of hardirq have the idle time already flushed from the hardirq entry. In the other cases we always account to system/irq time: * On hardirq exit we account the time to hardirq time. * On softirq exit we account the time to softirq time. To optimize this and avoid the indirect call to vtime_account() and the checks it performs, specialize the vtime irq APIs and only perform the check on irq entry. Irq exit can directly call vtime_account_system(). CONFIG_IRQ_TIME_ACCOUNTING behaviour doesn't change and directly maps to its own vtime_account() implementation. One may want to take benefits from the new APIs to optimize irq time accounting as well in the future. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
2012-10-30vtime: Make vtime_account_system() irqsafeFrederic Weisbecker1-1/+3
vtime_account_system() currently has only one caller with vtime_account() which is irq safe. Now we are going to call it from other places like kvm where irqs are not always disabled by the time we account the cputime. So let's make it irqsafe. The arch implementation part is now prefixed with "__". vtime_account_idle() arch implementation is prefixed accordingly to stay consistent. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Fenghua Yu <fenghua.yu@intel.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
2012-10-30vtime: Gather vtime declarations to their own header fileFrederic Weisbecker1-0/+22
These APIs are scattered around and are going to expand a bit. Let's create a dedicated header file for sanity. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Gortmaker <paul.gortmaker@windriver.com>