linux-kernel - Re: [RFC patch 1/2] sched: dynamically adapt granularity with nr

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Message-ID: <20100913064153.GB14728@elte.hu>
Date:	Mon, 13 Sep 2010 08:41:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Galbraith <efault@....de>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [RFC patch 1/2] sched: dynamically adapt granularity with
 nr_running


* Mike Galbraith <efault@....de> wrote:

> On Sun, 2010-09-12 at 14:16 -0400, Mathieu Desnoyers wrote:

> > Or am I missing your point ?
> 
> Yes and no.  I'm pondering the parent, but by the same token, the 
> vfork child shouldn't be penalized either.
> 
> Does your latency go down drastically if you turn START_DEBIT off? 
> Seems like it should.  Perhaps START_DEBIT should not start a task 
> further right than rightmost.  I've done that before.
> 
> maximum latency: 19221.5 µs
> average latency: 5159.0 µs
> missed timer events: 0
> 
> maximum latency: 43901.0 µs
> average latency: 8430.1 µs
> missed timer events: 0
> 
> Turning it off here cut latency roughly in half (i've piddled vfork 
> though, but not completely).  Limiting child placement to no further 
> right than rightmost should help quite a bit.

Very interesting observation. Mathieu, mind testing Mike's suggestion 
with wakeup-latency.c?

Thanks,

	Ingo
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