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Message-ID: <2f9131e4-1fdb-f80a-3b52-b98360164b3b@arm.com>
Date: Fri, 19 Jan 2024 15:00:45 +0000
From: James Clark <james.clark@....com>
To: Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>
Cc: linux-kernel@...r.kernel.org, Hector Martin <marcan@...can.st>,
Ian Rogers <irogers@...gle.com>, acme@...hat.com, john.g.garry@...cle.com,
leo.yan@...aro.org, linux-arm-kernel@...ts.infradead.org,
linux-perf-users@...r.kernel.org, mike.leach@...aro.org,
namhyung@...nel.org, suzuki.poulose@....com, tmricht@...ux.ibm.com,
will@...nel.org
Subject: Re: [PATCH] perf print-events: make is_event_supported() more robust
On 17/01/2024 09:05, Marc Zyngier wrote:
> Hi Mark,
>
> On Tue, 16 Jan 2024 17:03:48 +0000,
> Mark Rutland <mark.rutland@....com> wrote:
>>
>> Currently the perf tool doesn't deteect support for extneded event types
>> on Apple M1/M2 systems, and will not auto-expand plain PERF_EVENT_TYPE
>> hardware events into per-PMU events. This is due to the detection of
>> extended event types not handling mandatory filters required by the
>> M1/M2 PMU driver.
>
> Thanks for looking into this.
>
> I've given your patch a go on my M1 box, and it indeed makes things
> substantially better:
>
> $ sudo ./perf stat -e cycles ~/hackbench 100 process 1000
> Running with 100*40 (== 4000) tasks.
> Time: 3.419
>
> Performance counter stats for '/home/maz/hackbench 100 process 1000':
>
> 174,783,472,090 apple_firestorm_pmu/cycles/ (93.10%)
> 39,134,744,813 apple_icestorm_pmu/cycles/ (71.86%)
>
> 3.568145595 seconds time elapsed
>
> 12.203084000 seconds user
> 55.135271000 seconds sys
>
> However, I'm seeing some slightly odd behaviours:
>
> $ sudo ./perf stat -e cycles:k ~/hackbench 100 process 1000
> Running with 100*40 (== 4000) tasks.
> Time: 3.313
>
> Performance counter stats for '/home/maz/hackbench 100 process 1000':
>
> <not supported> apple_firestorm_pmu/cycles:k/
> <not supported> apple_icestorm_pmu/cycles:k/
>
> 3.467568841 seconds time elapsed
>
> 13.080111000 seconds user
> 53.162099000 seconds sys
>
> I would have expected it to count, but it didn't. For that to work, I
> have to add the 'H' modifier:
>
> $ sudo ./perf stat -e cycles:Hk ~/hackbench 100 process 1000
> Running with 100*40 (== 4000) tasks.
> Time: 3.335
>
> Performance counter stats for '/home/maz/hackbench 100 process 1000':
>
> 183,756,134,397 apple_firestorm_pmu/cycles:Hk/ (85.56%)
> 37,302,841,991 apple_icestorm_pmu/cycles:Hk/ (72.10%)
>
> 3.490138958 seconds time elapsed
>
> 13.376772000 seconds user
> 53.326289000 seconds sys
>
> But my perf-foo is as basic as it gets, so it is likely that I'm
> missing something.
>
> Thanks,
>
> M.
>
The default for exclude_guest=1 is always set unless you use "perf kvm
record". But unfortunately if you add _any_ modifier then all the
default values get overwritten, which is why adding k stops it from working.
It seems like a lot of the pain comes from the fact that the command
line modifiers are includes, and the kernel options are excludes.
Resulting in some complicated logic in get_event_modifier() to try to
work out what you wanted, which I suppose it got it wrong in this scenario.
Another thing is that evsel__detect_missing_features() only works to
remove arguments, where as for M1/M2 you want to _add_ exclude_guest
back in again. But maybe not if you started adding modifiers...
I don't really have an answer or a solution, but I was wondering if
there was a bug that could be fixed so I went to look.
My first thought was maybe we could ignore exclude_guest=0 on M1/M2
rather than returning an error. I don't think it would be too surprising
that guest samples are missing if they are never supported. Maybe the
exclude_guest argument is only useful if it actually has an effect,
rather than having an argument that always needs to be on anyway.
Or secondly maybe we could make get_event_modifier() interact with
evsel__detect_missing_features() but I can't imagine it being very
maintainable once we start adding a few interactions. And it's still
hard to predict what the user really wants given a single letter and
many exclude_* options.
James
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