Commit-ID: 24811637dbfd07c69da7e9db586d35d17e6afca3
Gitweb: https://git.kernel.org/tip/24811637dbfd07c69da7e9db586d35d17e6afca3
Author: Peter Zijlstra <pet...@infradead.org>
AuthorDate: Mon, 27 May 2019 10:23:26 +0200
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Mon, 3 Jun 2019 12:32:56 +0200
locking/lock_events: Use raw_cpu_{add,inc}() for stats
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) <pet...@infradead.org>
Acked-by: Linus Torvalds <torva...@linux-foundation.org>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: H. Peter Anvin <h...@zytor.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Tim Chen <tim.c.c...@linux.intel.com>
Cc: Waiman Long <long...@redhat.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: huang ying <huang.ying.cari...@gmail.com>
Link:
https://lkml.kernel.org/r/20190527082326.gp2...@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
kernel/locking/lock_events.h | 45 ++++----------------------------------------
1 file changed, 4 insertions(+), 41 deletions(-)
diff --git a/kernel/locking/lock_events.h b/kernel/locking/lock_events.h
index 46b71af8eef2..8c7e7d25f09c 100644
--- a/kernel/locking/lock_events.h
+++ b/kernel/locking/lock_events.h
@@ -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)
