Re: [PATCH v2] perf/x86/amd: Make HW_CACHE_REFERENCES and HW_CACHE_MISSES measure L2

From: Borislav Petkov
Date: Wed Aug 24 2016 - 10:56:01 EST

On Wed, Aug 24, 2016 at 02:12:08PM +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 and TLB fill
> requests to the L2 and instruction/data cache and TLB misses in the L2
> respectively. That way the events measure unified caches on both
> platforms.

I'm still not really sure about this: we can't really compare L3 to L2
access patterns - it is almost as comparing apples to oranges. Can we
use the Intel L2 events instead?

I mean, this makes much more sense to me because:

* you *actually* compare the same cache levels
* you have L2 *everywhere* vs L3 (and L4) which are sometimes not present on
thin clients

People who want LLC can enable them with -e additionally...



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