linux-kernel - Re: V4L2 drivers: potentially dangerous and inefficient msecs_to

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Message-ID: <4AAEBABA.9060108@gmail.com>
Date:	Mon, 14 Sep 2009 23:50:50 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Andreas Mohr <andi@...as.de>
CC:	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Luca Risolia <luca.risolia@...dio.unibo.it>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: V4L2 drivers: potentially dangerous and inefficient msecs_to_jiffies()
 calculation

On 09/14/2009 11:39 PM, Andreas Mohr wrote:
> On Mon, Sep 14, 2009 at 11:34:40PM +0200, Jiri Slaby wrote:
>> On 09/14/2009 11:07 PM, Andreas Mohr wrote:
>>> msecs_to_jiffies(1) is quite a bit too boldly assuming
>>> that all of the msecs_to_jiffies(x) implementation branches
>>> always round up.
>>
>> They do, don't they?
> 
> I'd hope so, but a slight risk remains, you never know,
> especially with 4+ or so variants...

A potential problem here is rather that it may wait longer due to
returning 1 jiffie. It's then timeout * 1000 * 1. On 250HZ system it
makes a difference of multiple of 4. Don't think it's a real issue in
those drivers at all, but it's worth fixing. Care to post a patch?
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