leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

locking/lock_events: Use raw_cpu_{add,inc}() for stats

Browse Source 
Instead of playing silly games with CONFIG_DEBUG_PREEMPT toggling
between this_cpu_*() and __this_cpu_*() use raw_cpu_*(), which is
exactly what we want here.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Link: https://lkml.kernel.org/r/20190527082326.GP2623@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2019-05-27 10:23:26 +02:00 committed by Ingo Molnar
parent d9349850e1
commit 24811637db
1 changed files with 4 additions and 41 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
kernel/locking/lock_events.h
View File

@ -31,50 +31,13 @@ enum lock_events {
DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]);
/*
* The purpose of the lock event counting subsystem is to provide a low
* overhead way to record the number of specific locking events by using
* percpu counters. It is the percpu sum that matters, not specifically
* how many of them happens in each cpu.
*
* It is possible that the same percpu counter may be modified in both
* the process and interrupt contexts. For architectures that perform
* percpu operation with multiple instructions, it is possible to lose
* count if a process context percpu update is interrupted in the middle
* and the same counter is updated in the interrupt context. Therefore,
* the generated percpu sum may not be precise. The error, if any, should
* be small and insignificant.
*
* For those architectures that do multi-instruction percpu operation,
* preemption in the middle and moving the task to another cpu may cause
* a larger error in the count. Again, this will be few and far between.
* Given the imprecise nature of the count and the possibility of resetting
* the count and doing the measurement again, this is not really a big
* problem.
*
* To get a better picture of what is happening under the hood, it is
* suggested that a few measurements should be taken with the counts
* reset in between to stamp out outliner because of these possible
* error conditions.
*
* To minimize overhead, we use __this_cpu_*() in all cases except when
* CONFIG_DEBUG_PREEMPT is defined. In this particular case, this_cpu_*()
* will be used to avoid the appearance of unwanted BUG messages.
*/
#ifdef CONFIG_DEBUG_PREEMPT
#define lockevent_percpu_inc(x) this_cpu_inc(x)
#define lockevent_percpu_add(x, v) this_cpu_add(x, v)
#else
#define lockevent_percpu_inc(x) __this_cpu_inc(x)
#define lockevent_percpu_add(x, v) __this_cpu_add(x, v)
#endif
/*
* Increment the PV qspinlock statistical counters
* Increment the statistical counters. use raw_cpu_inc() because of lower
* overhead and we don't care if we loose the occasional update.
*/
static inline void __lockevent_inc(enum lock_events event, bool cond)
{
if (cond)
lockevent_percpu_inc(lockevents[event]);
raw_cpu_inc(lockevents[event]);
}
#define lockevent_inc(ev) __lockevent_inc(LOCKEVENT_ ##ev, true)
@ -82,7 +45,7 @@ static inline void __lockevent_inc(enum lock_events event, bool cond)
static inline void __lockevent_add(enum lock_events event, int inc)
{
lockevent_percpu_add(lockevents[event], inc);
raw_cpu_add(lockevents[event], inc);
}
#define lockevent_add(ev, c) __lockevent_add(LOCKEVENT_ ##ev, c)