linux-kernel - Re: [PATCH 2/2] perf/x86/intel, watchdog: Switch NMI watchdog to ref cycles on x86

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Date:   Mon, 22 May 2017 14:03:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...el.com
Cc:     mingo@...hat.com, eranian@...gle.com, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, acme@...hat.com,
        jolsa@...hat.com, torvalds@...ux-foundation.org,
        tglx@...utronix.de, vincent.weaver@...ne.edu, ak@...ux.intel.com
Subject: Re: [PATCH 2/2] perf/x86/intel, watchdog: Switch NMI watchdog to ref
 cycles on x86

On Fri, May 19, 2017 at 10:06:22AM -0700, kan.liang@...el.com wrote:
> This patch was once merged, but reverted later.
> Because ref-cycles can not be used anymore when watchdog is enabled.
> The commit is 44530d588e142a96cf0cd345a7cb8911c4f88720
> 
> The patch 1/2 has extended the ref-cycles to GP counter. The concern
> should be gone.

So its not a problem if every Atom prior to Goldmont, and all Core/Core2
products regress?

P6 and P4 you've entirely broken, as they don't have REF_CPU_CYCLES at all.

So no, I don't think this is right even now.