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Date:   Wed, 18 May 2022 14:12:21 +0800
From:   Leo Yan <leo.yan@linaro.org>
To:     Adam Li <adamli@amperemail.onmicrosoft.com>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Like Xu <likexu@tencent.com>, Ian Rogers <irogers@google.com>,
        Alyssa Ross <hi@alyssa.is>, Kajol Jain <kjain@linux.ibm.com>,
        Li Huafei <lihuafei1@huawei.com>,
        German Gomez <german.gomez@arm.com>,
        James Clark <james.clark@arm.com>,
        Kan Liang <kan.liang@linux.intel.com>,
        Ali Saidi <alisaidi@amazon.com>,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 9/11] perf c2c: Sort on peer snooping for load
 operations
Message-ID: <20220518061221.GA430350@leoy-ThinkPad-X240s>
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 <20220508092346.255826-10-leo.yan@linaro.org>
 <fefc1f23-ea1c-6339-77c4-b0974cbd6e93@amperemail.onmicrosoft.com>
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Hi Adam,

On Fri, May 13, 2022 at 05:05:45PM +0800, Adam Li wrote:

[...]

> > As result, we can get the 'peer' display as below:
> > 
> >   # perf c2c report -d peer --coalesce tid,pid,iaddr,dso -N --stdio
> > 
> 
> Hi Leo,
> 
> I tested v2 patch on 2P Altra system.
> In case the false-sharing data is mainly from remote node, 'Snoop Peers'
> cannot indicate severity of false-sharing. As showed in bellow output,
> there are only 10 'Load HIT Peer' records, while there are 2353
> 'Load Remote DRAM' records.
> 
> And the name 'Load Remote DRAM' is kind of misleading, since we cannot tell
> the data source is 'DRAM'.

Appreicate for the testing, and your feedback is very helpful.

After some discussion, in the patch set v9 "perf: arm-spe: Decode SPE
source and use for perf c2c" (please ignore the typo "v8", actually
it's patch set v9), Ali has updated the memory tag setting for the
type ARM_SPE_NV_REMOTE.  I think the prominent change is we set
PERF_MEM_SNOOPX_PEER flag for remote access.

Please note, in the total statistics, all remote accesses will be
accounted into metric "rmt_hit", so "rmt_hit" includes the access for
remote DRAM or any upwards cache levels due we cannot distinguish
them.

From my experiment, with this updating the output result is promised
for the peer accesses and it's easier for inspecting false sharing.

As you might see I have prepared a git repo:
https://git.linaro.org/people/leo.yan/linux-spe.git/ branch:
perf_c2c_arm_spe_peer_v3, which contains the updated patches for both
memory flag setting and perf c2c related patches.

Could you confirm if the updated code works for you or not?

Thanks,
Leo