linux-kernel - Re: Active waiting with yield()

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Message-ID: <Pine.LNX.4.64.0811171228500.4019@hs20-bc2-1.build.redhat.com>
Date:	Mon, 17 Nov 2008 12:39:10 -0500 (EST)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, rml@...h9.net, Alasdair G Kergon <agk@...hat.com>,
	Milan Broz <mbroz@...hat.com>
Subject: Re: Active waiting with yield()

On Sat, 15 Nov 2008, Peter Zijlstra wrote:

> On Fri, 2008-11-14 at 16:41 -0500, Mikulas Patocka wrote:
> 
> > So, use msleep(1) instead of yield() ?
> 
> wait_event() of course!

Why? Why developes don't like active waiting when terminating a driver?
Is there any real workload when 1ms delay on driver unload would be 
problematic? Or don't they like it because of coding style?

L1 cache miss --- 10ns --- on every request, when using wait queues
msleep latency --- 1ms --- on driver termination, when using msleep
--- so if the driver processes more than 100000 requests between reboots, 
wait queues actually slow things down.

Mikulas
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