linux-kernel - Re: [PATCH] perf/x86/intel: Drop kernel samples even though :u is specified

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Message-ID: <20170519123648.p4tkt6xrt5xachuw@hirez.programming.kicks-ass.net>
Date:   Fri, 19 May 2017 14:36:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Jin, Yao" <yao.jin@...ux.intel.com>
Cc:     acme@...nel.org, jolsa@...nel.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] perf/x86/intel: Drop kernel samples even though :u is
 specified

On Fri, May 19, 2017 at 08:24:19PM +0800, Jin, Yao wrote:
> > Ah, I was more thinking of something like PERF_PMU_CAP_NO_SKID or
> > something that would skip the test and preserve current behaviour.
> 
> OK, I understand now. For example, for PEBS event, its capabilities should
> be set with PERF_PMU_CAP_NO_SKID.

Except you cannot in fact do that, since PEBS is the same struct pmu as
the normal counters (they share counter space after all).

Also, weren't there PEBS errata that would allow this to happen?

But no, more for other architectures to opt out for some reason. But I'm
thinking we want to start out by unconditionally doing this. It would be
good to try and Cc most arch pmu maintainers on this though, so they can
object.