Re: [PATCH][resubmit] x86: enable preemption in delay

Pavel Machek
2008-07-06T14:47:52Z

On Wed 2008-06-18 09:55:18, Ingo Molnar wrote:
>
> * Marin Mitov <mitov@issp.bas.bg> wrote:
>
> > Why not something like that (do keep in mind I am not an expert :-):
> >
> > static void delay_tsc(unsigned long loops)
> > {
> > get and store the mask of allowed cpus;
> > /* prevent the migration */
> > set the mask of allowed cpus to the current cpu only;
> > /* is it possible? could it be guaranteed? */
> > loop for the delay;
> > restore the old mask of allowed cpus;
> > }
> >
> > You have got the idea. Could it be realized? Is it more expensive than
> > the current realization? So, comments, please.
>
> hm, changing/saving/restorig cpus_allowed is really considered a 'heavy'
> operation compared to preempt_disable(). On a 4096 CPUs box cpus_allowed
> is 4096 bits which is half a kilobyte ...

Time to RLE the bitmap?

<runs> Pavel

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