linux-kernel - Re: [PATCH] posix clocks: replace mutex with reader/writer semaphore

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Message-ID: <20110414180458.GA24534@riccoc20.at.omicron.at>
Date:	Thu, 14 Apr 2011 20:04:59 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH] posix clocks: replace mutex with reader/writer
 semaphore

On Wed, Mar 30, 2011 at 03:41:40PM +0200, Thomas Gleixner wrote:
> On Wed, 30 Mar 2011, Richard Cochran wrote:
> 
> > A dynamic posix clock is protected from asynchronous removal by a mutex.
> > However, using a mutex has the unwanted effect that a long running clock
> > operation in one process will unnecessarily block other processes.
> > 
> > For example, one process might call read() to get an external time stamp
> > coming in at one pulse per second. A second process calling clock_gettime
> > would have to wait for almost a whole second.
> > 
> > This patch fixes the issue by using a reader/writer semaphore instead of
> > a mutex.
> 
> Yuck. /me wonders why we did not see that during the review :)

Thomas,

I don't see this in -rc3, but I think it should go in.
Can you please take this one?

Thanks,

Richard


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