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

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Message-ID: <20220326062303.GC20556@leoy-ThinkPad-X240s>
Date:   Sat, 26 Mar 2022 14:23:03 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Ali Saidi <alisaidi@...zon.com>
Cc:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, german.gomez@....com,
        acme@...nel.org, 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

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.

Thanks,
Leo

> +
>  			if (lvl & P(LVL, LOC_RAM) || lnum == P(LVLNUM, RAM)) {
>  				stats->lcl_dram++;
>  				if (snoop & P(SNOOP, HIT))
> -- 
> 2.32.0
>