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

[Rodolfo Giometti <giometti@enneenne.com>]

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@enneenne.com
Linux Device Driver                             giometti@gnudd.com
Embedded Systems                     		giometti@linux.it
UNIX programming                     phone:     +39 349 2432127
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