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authorUros Bizjak <ubizjak@gmail.com>2023-07-06 17:16:48 +0300
committerPeter Zijlstra <peterz@infradead.org>2023-07-10 10:52:35 +0300
commit4c1c9dea2089374cb58505a0df6136969ff3c8b9 (patch)
tree31ccb01e981ee0bf63342378bbd0f1e3c2ff3474
parent7c2128235eff99b448af8f4b5b2933495bf1a440 (diff)
downloadlinux-4c1c9dea2089374cb58505a0df6136969ff3c8b9.tar.xz
perf/x86: Use local64_try_cmpxchg
Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. No functional change intended. Cc. "H. Peter Anvin" <hpa@zytor.com> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20230706141720.2672-1-ubizjak@gmail.com
-rw-r--r--arch/x86/events/amd/ibs.c4
-rw-r--r--arch/x86/events/core.c10
-rw-r--r--arch/x86/events/intel/cstate.c10
-rw-r--r--arch/x86/events/msr.c8
4 files changed, 13 insertions, 19 deletions
diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 74e664266753..7d29be0a279b 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -156,8 +156,8 @@ perf_event_try_update(struct perf_event *event, u64 new_raw_count, int width)
* count to the generic event atomically:
*/
prev_raw_count = local64_read(&hwc->prev_count);
- if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
- new_raw_count) != prev_raw_count)
+ if (!local64_try_cmpxchg(&hwc->prev_count,
+ &prev_raw_count, new_raw_count))
return 0;
/*
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 9d248703cbdd..23c96420dea1 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -129,13 +129,11 @@ u64 x86_perf_event_update(struct perf_event *event)
* exchange a new raw count - then add that new-prev delta
* count to the generic event atomically:
*/
-again:
prev_raw_count = local64_read(&hwc->prev_count);
- rdpmcl(hwc->event_base_rdpmc, new_raw_count);
-
- if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
- new_raw_count) != prev_raw_count)
- goto again;
+ do {
+ rdpmcl(hwc->event_base_rdpmc, new_raw_count);
+ } while (!local64_try_cmpxchg(&hwc->prev_count,
+ &prev_raw_count, new_raw_count));
/*
* Now we have the new raw value and have updated the prev
diff --git a/arch/x86/events/intel/cstate.c b/arch/x86/events/intel/cstate.c
index 835862c548cc..97035db68df2 100644
--- a/arch/x86/events/intel/cstate.c
+++ b/arch/x86/events/intel/cstate.c
@@ -365,13 +365,11 @@ static void cstate_pmu_event_update(struct perf_event *event)
struct hw_perf_event *hwc = &event->hw;
u64 prev_raw_count, new_raw_count;
-again:
prev_raw_count = local64_read(&hwc->prev_count);
- new_raw_count = cstate_pmu_read_counter(event);
-
- if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
- new_raw_count) != prev_raw_count)
- goto again;
+ do {
+ new_raw_count = cstate_pmu_read_counter(event);
+ } while (!local64_try_cmpxchg(&hwc->prev_count,
+ &prev_raw_count, new_raw_count));
local64_add(new_raw_count - prev_raw_count, &event->count);
}
diff --git a/arch/x86/events/msr.c b/arch/x86/events/msr.c
index 0feaaa571303..61c59e0627d4 100644
--- a/arch/x86/events/msr.c
+++ b/arch/x86/events/msr.c
@@ -244,12 +244,10 @@ static void msr_event_update(struct perf_event *event)
s64 delta;
/* Careful, an NMI might modify the previous event value: */
-again:
prev = local64_read(&event->hw.prev_count);
- now = msr_read_counter(event);
-
- if (local64_cmpxchg(&event->hw.prev_count, prev, now) != prev)
- goto again;
+ do {
+ now = msr_read_counter(event);
+ } while (!local64_try_cmpxchg(&event->hw.prev_count, &prev, now));
delta = now - prev;
if (unlikely(event->hw.event_base == MSR_SMI_COUNT)) {