linux-kernel - Re: [PATCH v4 4/4] perf mem: Support HITM for when mem_lvl

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Message-ID: <Yj8Vd2vsw8yJ8b4x@kernel.org>
Date:   Sat, 26 Mar 2022 10:30:31 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Ali Saidi <alisaidi@...zon.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, german.gomez@....com,
        benh@...nel.crashing.org, Nick.Forrington@....com,
        alexander.shishkin@...ux.intel.com, andrew.kilroy@....com,
        james.clark@....com, john.garry@...wei.com, jolsa@...nel.org,
        kjain@...ux.ibm.com, lihuafei1@...wei.com, mark.rutland@....com,
        mathieu.poirier@...aro.org, mingo@...hat.com, namhyung@...nel.org,
        peterz@...radead.org, will@...nel.org
Subject: Re: [PATCH v4 4/4] perf mem: Support HITM for when mem_lvl_num is any

Em Sat, Mar 26, 2022 at 02:23:03PM +0800, Leo Yan escreveu:
> On Thu, Mar 24, 2022 at 06:33:23PM +0000, Ali Saidi wrote:
> > For loads that hit in a the LLC snoop filter and are fulfilled from a
> > higher level cache on arm64 Neoverse cores, it's not usually clear what
> > the true level of the cache the data came from (i.e. a transfer from a
> > core could come from it's L1 or L2). Instead of making an assumption of
> > where the line came from, add support for incrementing HITM if the
> > source is CACHE_ANY.
> > 
> > Since other architectures don't seem to populate the mem_lvl_num field
> > here there shouldn't be a change in functionality.
> > 
> > Signed-off-by: Ali Saidi <alisaidi@...zon.com>
> > Tested-by: German Gomez <german.gomez@....com>
> > Reviewed-by: German Gomez <german.gomez@....com>
> > ---
> >  tools/perf/util/mem-events.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/tools/perf/util/mem-events.c b/tools/perf/util/mem-events.c
> > index e5e405185498..084977cfebef 100644
> > --- a/tools/perf/util/mem-events.c
> > +++ b/tools/perf/util/mem-events.c
> > @@ -539,6 +539,15 @@ do {				\
> >  					stats->ld_llchit++;
> >  			}
> >  
> > +			/*
> > +			 * A hit in another cores cache must mean a llc snoop
> > +			 * filter hit
> > +			 */
> > +			if (lnum == P(LVLNUM, ANY_CACHE)) {
> > +				if (snoop & P(SNOOP, HITM))
> > +					HITM_INC(lcl_hitm);
> > +			}
> 
> This might break the memory profiling result for x86, see file
> arch/x86/events/intel/ds.c:
> 
>   97 void __init intel_pmu_pebs_data_source_skl(bool pmem)
>   98 {
>   99         u64 pmem_or_l4 = pmem ? LEVEL(PMEM) : LEVEL(L4);
>   ...
>  105         pebs_data_source[0x0d] = OP_LH | LEVEL(ANY_CACHE) | REM | P(SNOOP, HITM);
>  106 }
> 
> Which means that it's possible that it's a remote access and the cache
> level is ANY_CACHE, it's good to add checking for bit
> PERF_MEM_REMOTE_REMOTE:
> 
> 	u64 remote = data_src->mem_remote;
> 
> 	/*
> 	 * A hit in another cores cache must mean a llc snoop
> 	 * filter hit
> 	 */
> 	if (lnum == P(LVLNUM, ANY_CACHE) && remote != P(REMOTE, REMOTE)) {
> 	        if (snoop & P(SNOOP, HITM))
> 	                HITM_INC(lcl_hitm);
> 	}
> 
> Appreciate German's reviewing and testing, and sorry I jumped in very
> late.

I have not published this on perf/core, its just in tmp.perf/core while
tests ran, so I'll remove this specific patch and rerun tests, thanks
for reviewing.

- Arnaldo