linux-kernel - Re: [RFC] perf evlist: Warn if event group has mixed sw/hw events

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Date:   Mon, 26 Oct 2020 17:49:07 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Andi Kleen <ak@...ux.intel.com>, Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>,
        alexander.shishkin@...ux.intel.com
Subject: Re: [RFC] perf evlist: Warn if event group has mixed sw/hw events

Andi Kleen <ak@...ux.intel.com> writes:

> On Mon, Oct 26, 2020 at 11:19:37PM +0900, Namhyung Kim wrote:
>> This patch just added a warning before running it.  I'd really want to
>> fix the kernel if possible but don't have a good idea.  Thoughts?
>
> The easiest fix would be some multi threading in perf stat opening, then then
> extra latencies could be mostly hidden. One thread per group would probably
> be overkill, but just a few threads would lower the penalty significantly.
>
> I think that would be better than this patch and it's likely not that much
> more complicated, as this is already a lot of code.
>
>> +{
>> +	const char *known_sw_pmu[] = {
>> +		"software", "tracepoint", "breakpoint", "kprobe", "uprobe", "msr"
>
> That's a non scalable approach. New pmus get added regularly. It would be better to
> indicate this in a generic way from the kernel.

That, and also, intel_pt is a software PMU and a few of its features
depend on intel_pt/.../ being a group leader.

Regards,
--
Alex