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

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Message-ID: <20090915192146.GA18002@rhlx01.hs-esslingen.de>
Date:	Tue, 15 Sep 2009 21:21:46 +0200
From:	Andreas Mohr <andi@...as.de>
To:	Marcin Slusarz <marcin.slusarz@...il.com>
Cc:	Andreas Mohr <andi@...as.de>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Luca Risolia <luca.risolia@...dio.unibo.it>,
	linux-media@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	jirislaby@...il.com
Subject: Re: V4L2 drivers: potentially dangerous and inefficient
	msecs_to_jiffies() calculation

Hi,

On Tue, Sep 15, 2009 at 09:14:19PM +0200, Marcin Slusarz wrote:
> Andreas Mohr pisze:
> > ./drivers/media/video/zc0301/zc0301_core.c
> > do
> >                             cam->module_param.frame_timeout *
> >                             1000 * msecs_to_jiffies(1) );
> > multiple times each.
> > What they should do instead is
> > frame_timeout * msecs_to_jiffies(1000), I'd think.
> 
> Or better: frame_timeout * HZ

D'oh! ;-)

But then what about the other 3 bazillion places in the kernel
doing multiples of seconds?

linux-2.6.31]$ find . -name "*.c"|xargs grep msecs_to_jiffies|grep 1000|wc -l
73

If this expression is really better (also/especially from a maintenance POV),
then it should get changed.

> Marcin

Andreas Mohr
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