linux-kernel - Re: [PATCH 25/32] sched: introduce the finish_arch_pre_lock

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Date:	Fri, 29 Apr 2016 10:52:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	David Carrillo-Cisneros <davidcc@...gle.com>
Cc:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Tony Luck <tony.luck@...el.com>,
	Stephane Eranian <eranian@...gle.com>,
	Paul Turner <pjt@...gle.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 25/32] sched: introduce the finish_arch_pre_lock_switch()
 scheduler hook

On Thu, Apr 28, 2016 at 09:43:31PM -0700, David Carrillo-Cisneros wrote:
> This hook allows architecture specific code to be called at the end of
> the task switch and after perf_events' context switch but before the
> scheduler lock is released.
> 
> The specific use case in this series is to avoid multiple writes to a slow
> MSR until all functions which modify such register in task switch have
> finished.

Yeah, no. This really need way more justification. Why can't you use the
regular perf sched-in stuff for CQM?