Commit f1cac6ac authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

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



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: a4eaf7f1 ("perf: Rework the PMU methods")
Reported-by: default avatarDapeng Mi <dapeng1.mi@linux.intel.com>
Reported-by: default avatarIan Rogers <irogers@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarDapeng Mi <dapeng1.mi@linux.intel.com>
Link: https://patch.msgid.link/20260311204035.GX606826@noisy.programming.kicks-ass.net
parent 8d5fae60

arch/x86/events/core.c

+3 −1
Original line number Diff line number Diff line
@@ -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