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From:   Alexander Shishkin <alexander.shishkin@linux.intel.com>
To:     Andi Kleen <ak@linux.intel.com>, Namhyung Kim <namhyung@kernel.org>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Stephane Eranian <eranian@google.com>,
        Ian Rogers <irogers@google.com>,
        alexander.shishkin@linux.intel.com
Subject: Re: [RFC] perf evlist: Warn if event group has mixed sw/hw events
In-Reply-To: <20201026152108.GW466880@tassilo.jf.intel.com>
References: <20201026141937.582087-1-namhyung@kernel.org> <20201026152108.GW466880@tassilo.jf.intel.com>
Date:   Mon, 26 Oct 2020 17:49:07 +0200
Message-ID: <87y2jtq970.fsf@ashishki-desk.ger.corp.intel.com>
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Andi Kleen <ak@linux.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