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Date:   Thu, 29 Nov 2018 16:35:26 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andi Kleen <ak@linux.intel.com>
Cc:     Kyle Huey <me@kylehuey.com>, Kan Liang <kan.liang@linux.intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        Robert O'Callahan <robert@ocallahan.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Stephane Eranian <eranian@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vince Weaver <vincent.weaver@maine.edu>, acme@kernel.org,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [REGRESSION] x86, perf: counter freezing breaks rr
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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.