linux-kernel - Re: [RFC] perf: ref-cycle useless with watchdog changes

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Message-ID: <20160711103328.GI30154@twins.programming.kicks-ass.net>
Date:	Mon, 11 Jul 2016 12:33:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] perf: ref-cycle useless with watchdog changes

On Sun, Jul 10, 2016 at 11:48:11AM -0700, Stephane Eranian wrote:
> So we either redirect ref-cycles towards 0x013c
> (cpu_clk_unhalted:xlck) or another event maybe

Another solution is us introducing (another) fake event, say 0x0400,
which will have a constrained mask of: 0x0F | (6 << 32) and varies in
actual encoding depending on which counter it lands on.

That way we have more flexibility in scheduling the NMI watchdog, and
its exact period isn't _that_ important; although we could obviously
also fix up some of that if we wanted.