linux-kernel - Re: [PATCH] checkpatch: Add warnings for use of mdelay()

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Message-ID: <4C4F1846.3090103@codeaurora.org>
Date:	Tue, 27 Jul 2010 10:32:54 -0700
From:	Patrick Pannuto <ppannuto@...eaurora.org>
To:	Jonathan Corbet <corbet@....net>
CC:	Israel Schlesinger <israels@...eaurora.org>,
	linux-kernel@...r.kernel.org, apw@...onical.com,
	akpm@...ux-foundation.org, joe@...ches.com
Subject: Re: [PATCH] checkpatch: Add warnings for use of mdelay()

On 07/27/2010 10:31 AM, Jonathan Corbet wrote:
> On Tue, 27 Jul 2010 10:11:11 -0700
> Israel Schlesinger <israels@...eaurora.org> wrote:
> 
>> mdelay is a busy-wait loop which is wasteful. If at all possible,
>> callers should use msleep instead of mdelay.
>>
>> The only time mdelay is really appropriate is in atomic context,
>> however, delays of 1ms+ in atomic context are rather expensive, so
>> a warning for this case is probably appropriate as well to encourage
>> people to move such expensive delays outside of atomic context
> 
> Once upon a time, msleep(1) would sleep for 20ms, while mdelay(1) gave
> a 1ms delay.  My patch to fix msleep() at that time didn't get in due
> to concerns about the cost of using hrtimers.  Perhaps msleep() has
> gotten better, but, if not, actually getting a 1ms delay remains a
> valid reason for using mdelay() instead IMO.  It made a difference of a
> few seconds at open time for a driver I was doing at the time.
> 
> jon
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Check out the recently added usleep in -tip, and the checkpatch patch
pending in my queue that fixes that case (I'll send in a few hours ;) )

-pat

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
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