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x86/perf: Make sure to program the counter value for stopped events on migration

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Both Mi Dapeng and Ian Rogers noted that not everything that sets HES_STOPPED
is required to EF_UPDATE. Specifically the 'step 1' loop of rescheduling
explicitly does EF_UPDATE to ensure the counter value is read.

However, then 'step 2' simply leaves the new counter uninitialized when
HES_STOPPED, even though, as noted above, the thing that stopped them might not
be aware it needs to EF_RELOAD -- since it didn't EF_UPDATE on stop.

One such location that is affected is throttling, throttle does pmu->stop(, 0);
and unthrottle does pmu->start(, 0); possibly restarting an uninitialized counter.

Fixes: a4eaf7f146 ("perf: Rework the PMU methods")
Reported-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Reported-by: Ian Rogers <irogers@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://patch.msgid.link/20260311204035.GX606826@noisy.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2026-03-11 21:29:14 +01:00
parent 8d5fae6011
commit f1cac6ac62
1 changed files with 3 additions and 1 deletions
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4
arch/x86/events/core.c
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@ -1374,8 +1374,10 @@ static void x86_pmu_enable(struct pmu *pmu)
cpuc->events[hwc->idx] = event;
if (hwc->state & PERF_HES_ARCH)
if (hwc->state & PERF_HES_ARCH) {
static_call(x86_pmu_set_period)(event);
continue;
}
/*
* if cpuc->enabled = 0, then no wrmsr as