linux-kernel - Re: [PATCH 07/10] sched: Migrate sched to use new tick dependency mask model

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Message-ID: <20150810142847.GE16853@twins.programming.kicks-ass.net>
Date:	Mon, 10 Aug 2015 16:28:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Juri Lelli <juri.lelli@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 07/10] sched: Migrate sched to use new tick dependency
 mask model

On Mon, Aug 10, 2015 at 04:16:58PM +0200, Frederic Weisbecker wrote:

> I considered many times relying on hrtick btw but everyone seem to say it has a lot
> of overhead, especially due to clock reprogramming on schedule() calls.

Yeah, I have some vague ideas of how to take out much of that overhead
(tglx will launch frozen sharks at me I suspect), but we cannot get
around the overhead of actually having to program the hardware and that
is still a significant amount on many machines.

Supposedly machines with TSC deadline are better, but I've not tried
to benchmark that.
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