Messages in this thread Patch in this message | | | Date | Thu, 16 Feb 2023 15:35:19 +0100 | From | Janne Grunau <> | Subject | Re: [PATCH 1/2] arm_pmu: fix event CPU filtering |
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On 2023-02-16 14:12:38 +0000, Mark Rutland wrote: > Janne reports that perf has been broken on Apple M1 as of commit: > > bd27568117664b8b ("perf: Rewrite core context handling") > > That commit replaced the pmu::filter_match() callback with > pmu::filter(), whose return value has the opposite polarity, with true > implying events should be ignored rather than scheduled. While an > attempt was made to update the logic in armv8pmu_filter() and > armpmu_filter() accordingly, the return value remains inverted in a > couple of cases: > > * If the arm_pmu does not have an arm_pmu::filter() callback, > armpmu_filter() will always return whether the CPU is supported rather > than whether the CPU is not supported. > > As a result, the perf core will not schedule events on supported CPUs, > resulting in a loss of events. Additionally, the perf core will > attempt to schedule events on unsupported CPUs, but this will be > rejected by armpmu_add(), which may result in a loss of events from > other PMUs on those unsupported CPUs. > > * If the arm_pmu does have an arm_pmu::filter() callback, and > armpmu_filter() is called on a CPU which is not supported by the > arm_pmu, armpmu_filter() will return false rather than true. > > As a result, the perf core will attempt to schedule events on > unsupported CPUs, but this will be rejected by armpmu_add(), which may > result in a loss of events from other PMUs on those unsupported CPUs. > > This means a loss of events can be seen with any arm_pmu driver, but > with the ARMv8 PMUv3 driver (which is the only arm_pmu driver with an > arm_pmu::filter() callback) the event loss will be more limited and may > go unnoticed, which is how this issue evaded testing so far. > > Fix the CPU filtering by performing this consistently in > armpmu_filter(), and remove the redundant arm_pmu::filter() callback and > armv8pmu_filter() implementation. > > Commit bd2756811766 also silently removed the CHAIN event filtering from > armv8pmu_filter(), which will be addressed by a separate patch without > using the filter callback. > > Fixes: bd27568117664b8b ("perf: Rewrite core context handling") > Reported-by: Janne Grunau <j@jannau.net> > Link: https://lore.kernel.org/asahi/20230215-arm_pmu_m1_regression-v1-1-f5a266577c8d@jannau.net/ > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Ravi Bangoria <ravi.bangoria@amd.com> > Cc: Asahi Lina <lina@asahilina.net> > Cc: Eric Curtin <ecurtin@redhat.com> > --- > arch/arm64/kernel/perf_event.c | 7 ------- > drivers/perf/arm_pmu.c | 8 +------- > include/linux/perf/arm_pmu.h | 1 - > 3 files changed, 1 insertion(+), 15 deletions(-) > > diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c > index a5193f2146a6..3e43538f6b72 100644 > --- a/arch/arm64/kernel/perf_event.c > +++ b/arch/arm64/kernel/perf_event.c > @@ -1023,12 +1023,6 @@ static int armv8pmu_set_event_filter(struct hw_perf_event *event, > return 0; > } > > -static bool armv8pmu_filter(struct pmu *pmu, int cpu) > -{ > - struct arm_pmu *armpmu = to_arm_pmu(pmu); > - return !cpumask_test_cpu(smp_processor_id(), &armpmu->supported_cpus); > -} > - > static void armv8pmu_reset(void *info) > { > struct arm_pmu *cpu_pmu = (struct arm_pmu *)info; > @@ -1258,7 +1252,6 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name, > cpu_pmu->stop = armv8pmu_stop; > cpu_pmu->reset = armv8pmu_reset; > cpu_pmu->set_event_filter = armv8pmu_set_event_filter; > - cpu_pmu->filter = armv8pmu_filter; > > cpu_pmu->pmu.event_idx = armv8pmu_user_event_idx; > > diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c > index 9b593f985805..40f70f83daba 100644 > --- a/drivers/perf/arm_pmu.c > +++ b/drivers/perf/arm_pmu.c > @@ -550,13 +550,7 @@ static void armpmu_disable(struct pmu *pmu) > static bool armpmu_filter(struct pmu *pmu, int cpu) > { > struct arm_pmu *armpmu = to_arm_pmu(pmu); > - bool ret; > - > - ret = cpumask_test_cpu(cpu, &armpmu->supported_cpus); > - if (ret && armpmu->filter) > - return armpmu->filter(pmu, cpu); > - > - return ret; > + return !cpumask_test_cpu(cpu, &armpmu->supported_cpus); > } > > static ssize_t cpus_show(struct device *dev, > diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h > index ef914a600087..525b5d64e394 100644 > --- a/include/linux/perf/arm_pmu.h > +++ b/include/linux/perf/arm_pmu.h > @@ -100,7 +100,6 @@ struct arm_pmu { > void (*stop)(struct arm_pmu *); > void (*reset)(void *); > int (*map_event)(struct perf_event *event); > - bool (*filter)(struct pmu *pmu, int cpu); > int num_events; > bool secure_access; /* 32-bit ARM only */ > #define ARMV8_PMUV3_MAX_COMMON_EVENTS 0x40
This works as well. I limited the patch to the minimal fix this this late in the cycle.
Tested-by: Janne Grunau <j@jannau.net>
thanks, Janne
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