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

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Message-ID: <20170519121056.c45jbsfgcdjfuoow@hirez.programming.kicks-ass.net>
Date:   Fri, 19 May 2017 14:10:56 +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 08:06:09PM +0800, Jin, Yao wrote:
> SNIP
> 
> > I would much rather see this in generic code, somewhere around
> > __perf_event_overflow() I suppose. That would retain proper accounting
> > for the interrupt rate etc..
> > 
> > Also it would work for all architectures. Because I'm thinking more than
> > just x86 will suffer from skid.
> Yes, moving to generic code is better.  Thanks for the suggestion! I will do
> that.
> 
> > If you're really worried, I suppose you can put it behind a PERF_PMU_CAP
> > flag or something.
> I guess what you are suggesting is to add checking like:
> 
> if (is_sampling_event(event)) {
>     if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
>         return;
>     }
> }

Ah, I was more thinking of something like PERF_PMU_CAP_NO_SKID or
something that would skip the test and preserve current behaviour.