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