linux-kernel - Re: [RFC PATCH] check_preempt_tick should not compare vruntime with wall time

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Message-ID: <20100913181959.GB20171@elte.hu>
Date:	Mon, 13 Sep 2010 20:19:59 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Lindgren <tony@...mide.com>,
	Mike Galbraith <efault@....de>
Subject: Re: [RFC PATCH] check_preempt_tick should not compare vruntime with
 wall time


* Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> 2.0GHz Pentium M
> 
> * wakeup-latency.c (SIGEV_THREAD) with make -j10 
> 
> - Mainline 2.6.35.2 kernel
> 
> maximum latency: 45762.1 µs
> average latency: 7348.6 µs
> missed timer events: 0
> 
> - check_preempt fix
> 
> maximum latency: 39858.9 µs
> average latency: 7728.1 µs
> missed timer events: 0

Note that the check_preempt fix, as i mentioned it in the previous mail, 
has no effect on this workload - so any effect you see is pure noise.

> - With only Peter's smaller min_gran (shown below):
> 
> maximum latency: 29100.6 µs
> average latency: 6684.1 µs
> missed timer events: 0

That's the real improvement.

> - check_preempt fix + Peter's smaller min_gran:
> maximum latency: 20433.0 µs
> average latency: 5112.5 µs
> missed timer events: 0

Again, pure noise effect.

	Ingo
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