linux-kernel - Re: x86: disable preemption in delay

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Message-ID: <20071116071708.GA2103@elte.hu>
Date:	Fri, 16 Nov 2007 08:17:08 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: x86: disable preemption in delay_tsc()


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> It sounds like it would work OK.  What is the setup cost for a usleep?  
> I'd have thought that code which does something like
> 
> 	while (i++ < 1000) {
> 		foo();
> 		udelay(1);
> 	}
> 
> would take qiute a bit longer with such a change?

full roundtrip cost ought to be below 10 usecs, depending on the system. 
There's no problem doing a non-preemptible udelay up to 10 usecs and we 
could use usleep above that.

	Ingo
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