linux-kernel - Re: [PATCH v5 2/5] perf: Add SNOOP_PEER flag to perf mem data struct

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Message-ID: <c17dedde-6ba8-db9b-4827-32477f039764@linux.intel.com>
Date:   Fri, 22 Apr 2022 17:08:34 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Ali Saidi <alisaidi@...zon.com>
Cc:     Nick.Forrington@....com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, andrew.kilroy@....com,
        benh@...nel.crashing.org, german.gomez@....com,
        james.clark@....com, john.garry@...wei.com, jolsa@...nel.org,
        kjain@...ux.ibm.com, leo.yan@...aro.org, lihuafei1@...wei.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, mark.rutland@....com,
        mathieu.poirier@...aro.org, mingo@...hat.com, namhyung@...nel.org,
        peterz@...radead.org, will@...nel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v5 2/5] perf: Add SNOOP_PEER flag to perf mem data struct



On 4/22/2022 2:49 PM, Ali Saidi wrote:
> On Wed, 20 Apr 2022 18:43:28, Kan Liang wrote:
>> On 4/8/2022 3:53 PM, Ali Saidi wrote:
>>> Add a flag to the perf mem data struct to signal that a request caused a
>>> cache-to-cache transfer of a line from a peer of the requestor and
>>> wasn't sourced from a lower cache level.
>>
>> It sounds similar to the Forward state. Why can't the
>> PERF_MEM_SNOOPX_FWD be reused?
> 
> Is there a definition of SNOOPX_FWD i can refer to? Happy to use this instead if
> the semantics align between architectures.
> 

+ Andi

As my understanding, the SNOOPX_FWD means the Forward state, which is a 
non-modified (clean) cache-to-cache copy.
https://en.wikipedia.org/wiki/MESIF_protocol

Thanks,
Kan