Re: [PATCH v4 4/4] perf mem: Support HITM for when mem_lvl_num is any

From: Leo Yan <leo.yan@linaro.org>
To: Ali Saidi <alisaidi@amazon.com>
Cc: linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, german.gomez@arm.com,
	acme@kernel.org, benh@kernel.crashing.org,
	Nick.Forrington@arm.com, alexander.shishkin@linux.intel.com,
	andrew.kilroy@arm.com, james.clark@arm.com,
	john.garry@huawei.com, jolsa@kernel.org, kjain@linux.ibm.com,
	lihuafei1@huawei.com, mark.rutland@arm.com,
	mathieu.poirier@linaro.org, mingo@redhat.com,
	namhyung@kernel.org, peterz@infradead.org, will@kernel.org
Subject: Re: [PATCH v4 4/4] perf mem: Support HITM for when mem_lvl_num is any
Date: Sat, 26 Mar 2022 14:23:03 +0800	[thread overview]
Message-ID: <20220326062303.GC20556@leoy-ThinkPad-X240s> (raw)
In-Reply-To: <20220324183323.31414-5-alisaidi@amazon.com>

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@amazon.com>
> Tested-by: German Gomez <german.gomez@arm.com>
> Reviewed-by: German Gomez <german.gomez@arm.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
> 

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