linux-kernel - Re: why kernel implement "udelay" by cpu instructions?

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Message-ID: <4AF18CD9.40201@redhat.com>
Date:	Wed, 04 Nov 2009 09:16:57 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Bryan Donlan <bdonlan@...il.com>
CC:	Rajat Jain <Rajat.Jain@...ogain.com>, loody <miloody@...il.com>,
	linux-kernel@...r.kernel.org,
	Kernel Newbies <kernelnewbies@...linux.org>
Subject: Re: why kernel implement "udelay" by cpu instructions?

On 11/04/2009 12:36 AM, Bryan Donlan wrote:

> I thought hrtimers allow higher-precision wakeups these days?
> Of course, if you only want to sleep for a few microseconds, the
> context switch might take longer than you want to sleep...

Also, you may not be in a context where you can schedule.

Sometimes drivers need to implement a small delay (to wait
for something on the device) while holding a spinlock or
while interrupts are disabled.

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