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

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 74e664266753fc3544b0539e4b0b8629ed15b25d..7d29be0a279bb0885065322ed532dfe53ef75688 100644 (file)
--- 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 9d248703cbddcd6fb7623d22f4a408adee8d97d5..23c96420dea1c5b0eb2de66279fdb36afb63112b 100644 (file)
--- 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 835862c548ccb148854fa0cfcb318197c1097f1e..97035db68df208052883fe3ba65a3a75789b9ddb 100644 (file)
--- 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 0feaaa5713032ba3669a5a0c990b6e9a6871e976..61c59e0627d46644e2b436fab4ef5f0d191e5bd1 100644 (file)
--- 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)) {