Messages in this thread | | | Date | Wed, 18 Jun 2008 06:13:45 -0600 | From | "Gregory Haskins" <> | Subject | Re: [PATCH][resubmit] x86: enable preemption in delay |
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>>> On Wed, Jun 18, 2008 at 8:08 AM, in message <4858C286.BA47.005A.0@novell.com>, "Gregory Haskins" <ghaskins@novell.com> wrote: >>>> On Wed, Jun 18, 2008 at 3:55 AM, in message <20080618075518.GD4135@elte.hu>, > Ingo Molnar <mingo@elte.hu> 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 ... >> >> preempt_disable()/enable() on the other hand only touches a single >> variable, (thread_info->preempt_count which is an u32) >> >> Ingo > > FWIW: I had submitted some "migration disable" patches a while back that > would solve this without the cpus_allowed manipulations described here. Its > more expensive than a preempt-disable (but its preemptible), yet its way > cheaper (and more correct / less racy) than chaning cpus_allowed. I could > resubmit if there was any interest, though I think Ingo said he didnt like > the concept on the first pass. Anyway, FYI.
Sorry, should have provided a reference:
http://lkml.org/lkml/2008/2/12/344
> > -Greg > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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