Messages in this thread | | | Subject | Re: [PATCH] arm64: perf: Fix 64-bit event counter read truncation | From | Alexandru Elisei <> | Date | Wed, 10 Mar 2021 10:53:36 +0000 |
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Hi Rob,
On 3/10/21 12:44 AM, Rob Herring wrote: > Commit 0fdf1bb75953 ("arm64: perf: Avoid PMXEV* indirection") changed > armv8pmu_read_evcntr() to return a u32 instead of u64. The result is > silent truncation of the event counter when using 64-bit counters. Given > the offending commit appears to have passed thru several folks, it seems > likely this was a bad rebase after v8.5 PMU 64-bit counters landed.
Thank you for the fix, it does seem that I made a mistake when rebasing the series. Version v4 of the PMU NMI series was sent in 2019, then patch 8673e02e5841 ("arm64: perf: Add support for ARMv8.5-PMU 64-bit counters") from March 2020 changed the read of PMEVCNTR_EL0 to return an u64, then version v5 from June 2020 changed it back to returning an u32.
The result of read_pmvevcntr() is returned by armv8pmu_read_evcntr(), and it is an unsigned long which is 64bits for arm64, so the patch looks good to me:
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Thanks,
Alex
> > Fixes: 0fdf1bb75953 ("arm64: perf: Avoid PMXEV* indirection") > Cc: Alexandru Elisei <alexandru.elisei@arm.com> > Cc: Julien Thierry <julien.thierry.kdev@gmail.com> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Arnaldo Carvalho de Melo <acme@kernel.org> > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > Cc: Jiri Olsa <jolsa@redhat.com> > Cc: Namhyung Kim <namhyung@kernel.org> > Signed-off-by: Rob Herring <robh@kernel.org> > --- > arch/arm64/kernel/perf_event.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c > index 7d2318f80955..4658fcf88c2b 100644 > --- a/arch/arm64/kernel/perf_event.c > +++ b/arch/arm64/kernel/perf_event.c > @@ -460,7 +460,7 @@ static inline int armv8pmu_counter_has_overflowed(u32 pmnc, int idx) > return pmnc & BIT(ARMV8_IDX_TO_COUNTER(idx)); > } > > -static inline u32 armv8pmu_read_evcntr(int idx) > +static inline u64 armv8pmu_read_evcntr(int idx) > { > u32 counter = ARMV8_IDX_TO_COUNTER(idx); >
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