linux-kernel - Re: [PATCH] LinuxPPS (with new syscalls API)

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Message-ID: <20070711104611.GA16703@enneenne.com>
Date:	Wed, 11 Jul 2007 12:46:11 +0200
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] LinuxPPS (with new syscalls API) - new version

On Wed, Jul 11, 2007 at 10:17:47AM +0100, David Woodhouse wrote:
> On Tue, 2007-07-10 at 18:38 +0200, Rodolfo Giometti wrote:
> > On Tue, Jul 10, 2007 at 05:05:47PM +0100, David Woodhouse wrote:
> > > 
> > > I'm sure the version with 'volatile' will also be broken then. Sounds
> > > like the right answer is to fix the locking.
> > 
> > But wish avoiding locking at all since this may delay the time stamp
> > recording. We (the LinuxPPS guys) niticed that just a single
> > instruction my degrade the time setting about 50%!
> > 
> > I avoid locking just using a pointer and setting it to a dummy
> > structure when not used... is that wrong? :-o
> 
> Almost certainly (admittedly said without looking).

Please take a look at the code. I'm quite sure that it's ok. :)

I just set a pointer to a dummy struct or a valid one. By doing like
this I don't need a lock in the irq handler since it writes always
into a valid area. At non irq time I simply use a mutex lock.

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail:    giometti@...eenne.com
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Embedded Systems                     		giometti@...ux.it
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