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Message-ID: <64c2808e-ac2b-41c0-9e98-61b22e3031c1@linux.intel.com>
Date:   Wed, 13 Dec 2023 11:17:47 -0500
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Subject: Re: [PATCH V2 3/5] perf mem: Clean up perf_mem_events__name()
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To:     Leo Yan <leo.yan@linaro.org>
Cc:     acme@kernel.org, irogers@google.com, peterz@infradead.org,
        mingo@redhat.com, namhyung@kernel.org, jolsa@kernel.org,
        adrian.hunter@intel.com, john.g.garry@oracle.com, will@kernel.org,
        james.clark@arm.com, mike.leach@linaro.org,
        yuhaixin.yhx@linux.alibaba.com, renyu.zj@linux.alibaba.com,
        tmricht@linux.ibm.com, ravi.bangoria@amd.com,
        linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
References: <20231207192338.400336-1-kan.liang@linux.intel.com>
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 <20231209054809.GB2116834@leoy-yangtze.lan>
 <3b67c2de-741d-4d5e-8c8f-87b8b9e08825@linux.intel.com>
 <20231213133336.GA3895246@leoy-yangtze.lan>
From:   "Liang, Kan" <kan.liang@linux.intel.com>
In-Reply-To: <20231213133336.GA3895246@leoy-yangtze.lan>
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On 2023-12-13 8:33 a.m., Leo Yan wrote:
>>> I am a bit suspect if we really need the field '.aux_event', the
>>> '.aux_event' field is only used for generating event string.
>> No, it stores the event encoding for the extra event.
>> ARM doesn't need it, so it's 0.
> I searched a bit and confirmed '.aux_event' is only used in
> util/mem-events.c and for 'perf record'.
> 
> I failed to connect the code with "it stores the event encoding for the
> extra event".  Could you elaborate a bit for this?

The details of the reason of introducing the mem_load aux event can be
found here.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=61b985e3e775a3a75fda04ce7ef1b1aefc4758bc

A mem_load_aux event is a new requirement for SPR. For the other Intel
platforms, a single mem_load event is good enough to collect the data
source information. But for SPR, we have to group both the mem_load
event and the mem_load_aux event when collecting the data source
information. In the group, the mem_load_aux event must be the leader
event. But for the sample read case, only the sampling of the mem_load
make sense. So the is_mem_loads_aux_event() is introduced to switch the
sampling event to the mem_load event. Here is the perf tool patch.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2a57d40832dc8366bc517bcbbfdb1d7fb583735b

The .aux_event is to store the event encoding of the mem_load_aux event.
If it's the leader of a sampling read group, we should use the second
event as a sampling event.

Thanks,
Kan