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author | Joel Fernandes (Google) <joel@joelfernandes.org> | 2018-07-31 01:24:22 +0300 |
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committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2018-07-31 02:13:03 +0300 |
commit | e6753f23d961d601dbae50a2fc2a3975c9715b14 (patch) | |
tree | 54adb707018682f6b6f49a42273ca88012a829b0 /include/linux | |
parent | 01f38497c6f6525f57eb445887b9ed1867dbd05c (diff) | |
download | linux-e6753f23d961d601dbae50a2fc2a3975c9715b14.tar.xz |
tracepoint: Make rcuidle tracepoint callers use SRCU
In recent tests with IRQ on/off tracepoints, a large performance
overhead ~10% is noticed when running hackbench. This is root caused to
calls to rcu_irq_enter_irqson and rcu_irq_exit_irqson from the
tracepoint code. Following a long discussion on the list [1] about this,
we concluded that srcu is a better alternative for use during rcu idle.
Although it does involve extra barriers, its lighter than the sched-rcu
version which has to do additional RCU calls to notify RCU idle about
entry into RCU sections.
In this patch, we change the underlying implementation of the
trace_*_rcuidle API to use SRCU. This has shown to improve performance
alot for the high frequency irq enable/disable tracepoints.
Test: Tested idle and preempt/irq tracepoints.
Here are some performance numbers:
With a run of the following 30 times on a single core x86 Qemu instance
with 1GB memory:
hackbench -g 4 -f 2 -l 3000
Completion times in seconds. CONFIG_PROVE_LOCKING=y.
No patches (without this series)
Mean: 3.048
Median: 3.025
Std Dev: 0.064
With Lockdep using irq tracepoints with RCU implementation:
Mean: 3.451 (-11.66 %)
Median: 3.447 (-12.22%)
Std Dev: 0.049
With Lockdep using irq tracepoints with SRCU implementation (this series):
Mean: 3.020 (I would consider the improvement against the "without
this series" case as just noise).
Median: 3.013
Std Dev: 0.033
[1] https://patchwork.kernel.org/patch/10344297/
[remove rcu_read_lock_sched_notrace as its the equivalent of
preempt_disable_notrace and is unnecessary to call in tracepoint code]
Link: http://lkml.kernel.org/r/20180730222423.196630-3-joel@joelfernandes.org
Cleaned-up-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ Simplified WARN_ON_ONCE() ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'include/linux')
-rw-r--r-- | include/linux/tracepoint.h | 40 |
1 files changed, 32 insertions, 8 deletions
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index 19a690b559ca..d9a084c72541 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -15,6 +15,7 @@ */ #include <linux/smp.h> +#include <linux/srcu.h> #include <linux/errno.h> #include <linux/types.h> #include <linux/cpumask.h> @@ -33,6 +34,8 @@ struct trace_eval_map { #define TRACEPOINT_DEFAULT_PRIO 10 +extern struct srcu_struct tracepoint_srcu; + extern int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data); extern int @@ -75,10 +78,16 @@ int unregister_tracepoint_module_notifier(struct notifier_block *nb) * probe unregistration and the end of module exit to make sure there is no * caller executing a probe when it is freed. */ +#ifdef CONFIG_TRACEPOINTS static inline void tracepoint_synchronize_unregister(void) { + synchronize_srcu(&tracepoint_srcu); synchronize_sched(); } +#else +static inline void tracepoint_synchronize_unregister(void) +{ } +#endif #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS extern int syscall_regfunc(void); @@ -129,18 +138,31 @@ extern void syscall_unregfunc(void); * as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just * "void *data", where as the DECLARE_TRACE() will pass in "void *data, proto". */ -#define __DO_TRACE(tp, proto, args, cond, rcucheck) \ +#define __DO_TRACE(tp, proto, args, cond, rcuidle) \ do { \ struct tracepoint_func *it_func_ptr; \ void *it_func; \ void *__data; \ + int __maybe_unused idx = 0; \ \ if (!(cond)) \ return; \ - if (rcucheck) \ - rcu_irq_enter_irqson(); \ - rcu_read_lock_sched_notrace(); \ - it_func_ptr = rcu_dereference_sched((tp)->funcs); \ + \ + /* srcu can't be used from NMI */ \ + WARN_ON_ONCE(rcuidle && in_nmi()); \ + \ + /* keep srcu and sched-rcu usage consistent */ \ + preempt_disable_notrace(); \ + \ + /* \ + * For rcuidle callers, use srcu since sched-rcu \ + * doesn't work from the idle path. \ + */ \ + if (rcuidle) \ + idx = srcu_read_lock_notrace(&tracepoint_srcu); \ + \ + it_func_ptr = rcu_dereference_raw((tp)->funcs); \ + \ if (it_func_ptr) { \ do { \ it_func = (it_func_ptr)->func; \ @@ -148,9 +170,11 @@ extern void syscall_unregfunc(void); ((void(*)(proto))(it_func))(args); \ } while ((++it_func_ptr)->func); \ } \ - rcu_read_unlock_sched_notrace(); \ - if (rcucheck) \ - rcu_irq_exit_irqson(); \ + \ + if (rcuidle) \ + srcu_read_unlock_notrace(&tracepoint_srcu, idx);\ + \ + preempt_enable_notrace(); \ } while (0) #ifndef MODULE |