linux-kernel - Re: [RFC 00/11] perf: Enhancing perf to export processor hazard information

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Date:   Thu, 19 Mar 2020 22:22:03 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Kim Phillips <kim.phillips@....com>, maddy <maddy@...ux.ibm.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     Stephane Eranian <eranian@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linuxppc-dev@...ts.ozlabs.org, LKML <linux-kernel@...r.kernel.org>,
        Paul Mackerras <paulus@...ba.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Liang\, Kan" <kan.liang@...ux.intel.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        yao.jin@...ux.intel.com, Robert Richter <robert.richter@....com>
Subject: Re: [RFC 00/11] perf: Enhancing perf to export processor hazard information

Kim Phillips <kim.phillips@....com> writes:
> On 3/17/20 1:50 AM, maddy wrote:
>> On 3/13/20 4:08 AM, Kim Phillips wrote:
>>> On 3/11/20 11:00 AM, Ravi Bangoria wrote:
>>>
>>>> information on each sample using PMI at periodic intervals. Hence proposing
>>>> PERF_SAMPLE_PIPELINE_HAZ.
>>>
>>> And that's fine for any extra bits that POWER9 has to convey
>>> to its users beyond things already represented by other sample
>>> types like PERF_SAMPLE_DATA_SRC, but the capturing of both POWER9
>>> and other vendor e.g., AMD IBS data can be made vendor-independent
>>> at record time by using SAMPLE_AUX, or SAMPLE_RAW even, which is
>>> what IBS currently uses.
>> 
>> My bad. Not sure what you mean by this. We are trying to abstract
>> as much vendor specific data as possible with this (like perf-mem).
>
> Perhaps if I say it this way: instead of doing all the 
> isa207_get_phazard_data() work past the mfspr(SPRN_SIER)
> in patch 4/11, rather/instead just put the raw sier value in a 
> PERF_SAMPLE_RAW or _AUX event, and call perf_event_update_userpage.
> Specific SIER capabilities can be written as part of the perf.data
> header.  Then synthesize the true pipe events from the raw SIER
> values later, and in userspace.

In the past the perf maintainers have wanted the perf API to abstract
over the specific CPU details, rather than just pushing raw register
values out to userspace.

But maybe that's no longer the case and we should just use
PERF_SAMPLE_AUX?

cheers