linux-kernel - Re: [PATCH v2 9/11] perf c2c: Sort on peer snooping for load operations

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Date:   Wed, 18 May 2022 14:12:21 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Adam Li <adamli@...eremail.onmicrosoft.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Like Xu <likexu@...cent.com>, Ian Rogers <irogers@...gle.com>,
        Alyssa Ross <hi@...ssa.is>, Kajol Jain <kjain@...ux.ibm.com>,
        Li Huafei <lihuafei1@...wei.com>,
        German Gomez <german.gomez@....com>,
        James Clark <james.clark@....com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Ali Saidi <alisaidi@...zon.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 9/11] perf c2c: Sort on peer snooping for load
 operations

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