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Date:   Mon, 25 Apr 2022 13:01:40 -0400
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Subject: Re: [PATCH v5 2/5] perf: Add SNOOP_PEER flag to perf mem data struct
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To:     Leo Yan <leo.yan@linaro.org>, Andi Kleen <ak@linux.intel.com>
Cc:     Ali Saidi <alisaidi@amazon.com>, Nick.Forrington@arm.com,
        acme@kernel.org, alexander.shishkin@linux.intel.com,
        andrew.kilroy@arm.com, benh@kernel.crashing.org,
        german.gomez@arm.com, james.clark@arm.com, john.garry@huawei.com,
        jolsa@kernel.org, kjain@linux.ibm.com, lihuafei1@huawei.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org, mark.rutland@arm.com,
        mathieu.poirier@linaro.org, mingo@redhat.com, namhyung@kernel.org,
        peterz@infradead.org, will@kernel.org
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From:   "Liang, Kan" <kan.liang@linux.intel.com>
In-Reply-To: <20220424114302.GB978927@leoy-ThinkPad-X240s>
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On 4/24/2022 7:43 AM, Leo Yan wrote:
> On Sat, Apr 23, 2022 at 05:53:28AM -0700, Andi Kleen wrote:
>>
>>> Except SNOOPX_FWD means a no modified cache snooping, it also means it's
>>> a cache conherency from *remote* socket.  This is quite different from we
>>> define SNOOPX_PEER, which only snoop from peer CPU or clusters.
>>>

The FWD doesn't have to be *remote*. The definition you quoted is just 
for the "L3 Miss", which is indeed a remote forward. But we still have 
cross-core FWD. See Table 19-101.

Actually, X86 uses the PERF_MEM_REMOTE_REMOTE + PERF_MEM_SNOOPX_FWD to 
indicate the remote FWD, not just SNOOPX_FWD.

>>> If no objection, I prefer we could keep the new snoop type SNOOPX_PEER,
>>> this would be easier for us to distinguish the semantics and support the
>>> statistics for SNOOPX_FWD and SNOOPX_PEER separately.
>>>
>>> I overlooked the flag SNOOPX_FWD, thanks a lot for Kan's reminding.
>>
>> Yes seems better to keep using a separate flag if they don't exactly match.
>>

Yes, I agree with Andi. If you still think the existing flag combination 
doesn't match your requirement, a new separate flag should be 
introduced. I'm not familiar with ARM. I think I will leave it to you 
and the maintainer to decide.

Thanks,
Kan