linux-kernel - Re: [REGRESSION] x86, perf: counter freezing breaks rr

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Message-ID: <20181129153526.GR2131@hirez.programming.kicks-ass.net>
Date:   Thu, 29 Nov 2018 16:35:26 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Kyle Huey <me@...ehuey.com>, Kan Liang <kan.liang@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Robert O'Callahan <robert@...llahan.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Stephane Eranian <eranian@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vince Weaver <vincent.weaver@...ne.edu>, acme@...nel.org,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION] x86, perf: counter freezing breaks rr

On Tue, Nov 27, 2018 at 03:36:15PM -0800, Andi Kleen wrote:
> > It does seem that FREEZE_PERFMON_ON_PMI (misnamed as it is) is of
> > rather limited use (or even negative, in our case) to a counter that's
> > already restricted to ring 3.
> 
> It's much faster. The PMI cost goes down dramatically.

faster doesn't mean much when its broken.