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SubjectRe: [PATCH] perf/x86/amd: Make HW_CACHE_REFERENCES and HW_CACHE_MISSES measure L2
On Thu, 11 Aug, at 06:41:50PM, Borislav Petkov wrote:
> Drop stable from CC.
>
> On Thu, Aug 11, 2016 at 04:21:42PM +0100, Matt Fleming wrote:
> > While the Intel PMU monitors the LLC when perf enables the
> > HW_CACHE_REFERENCES and HW_CACHE_MISSES events, these events monitor
> > L1 instruction cache fetches (0x0080) and instruction cache misses
> > (0x0081) on the AMD PMU.
> >
> > This is extremely confusing when monitoring the same workload across
> > Intel and AMD machines, since parameters like,
> >
> > $ perf stat -e cache-references,cache-misses
> >
> > measure completely different things.
> >
> > Instead, make the AMD PMU measure instruction/data cache fill requests
> > to the L2 and instruction/data cache misses in the L2 when
> > HW_CACHE_REFERENCES and HW_CACHE_MISSES are enabled, respectively.
> > That way the events measure unified caches on both platforms.
>
> I guess that's closer.
>
> Even though LLC is not always L2 on AMD (some have L3). Btw,
> what are the exact events for PERF_COUNT_HW_CACHE_REFERENCES and
> PERF_COUNT_HW_CACHE_MISSES called on Intel?

They're referred to as "LLC Reference" and "LLC Misses" in the Intel
SDM Table 18-1 and "Longest latency cache references/misses" in Table
19-1.

> I could try to find better/more fitting event selectors on AMD...

If you've got any other suggestions, I'm all ears. Note that one thing
I wasn't sure about was whether we want to include TLB events hitting
the L2. I left them out of this patch, but it might make sense to add
them so that HW_CACHE_{REFERENCES,MISSES} is actually distinguishable
from LLC-{loads,misses}.

> > Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Borislav Petkov <bp@alien8.de>
> > Cc: <stable@vger.kernel.org>
> > ---
> > arch/x86/events/amd/core.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
> > index e07a22bb9308..8fd8bf79f32b 100644
> > --- a/arch/x86/events/amd/core.c
> > +++ b/arch/x86/events/amd/core.c
> > @@ -119,8 +119,8 @@ static const u64 amd_perfmon_event_map[PERF_COUNT_HW_MAX] =
> > {
> > [PERF_COUNT_HW_CPU_CYCLES] = 0x0076,
> > [PERF_COUNT_HW_INSTRUCTIONS] = 0x00c0,
> > - [PERF_COUNT_HW_CACHE_REFERENCES] = 0x0080,
> > - [PERF_COUNT_HW_CACHE_MISSES] = 0x0081,
> > + [PERF_COUNT_HW_CACHE_REFERENCES] = 0x037d,
> > + [PERF_COUNT_HW_CACHE_MISSES] = 0x037e,
> > [PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = 0x00c2,
> > [PERF_COUNT_HW_BRANCH_MISSES] = 0x00c3,
> > [PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = 0x00d0, /* "Decoder empty" event */
>
> Btw, there's also amd_event_mapping in arch/x86/kvm/pmu_amd.c which has
> duplicated amd_perfmon_event_map. Would need adjusting too.

Urgh, right. I totally missed that. I'll update.

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