lkml.org 
[lkml]   [2011]   [Mar]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC 2/2] Make x86 calibrate_delay run in parallel.

* Ingo Molnar <mingo@elte.hu> wrote:

>
> * Yinghai Lu <yinghai@kernel.org> wrote:
>
> > On Tue, Dec 14, 2010 at 5:58 PM, <Robin@sgi.com> wrote:
> > >
> > > On a 4096 cpu machine, we noticed that 318 seconds were taken for bringing
> > > up the cpus.  By specifying lpj=<value>, we reduced that to 75 seconds.
> > > Andi Kleen suggested we rework the calibrate_delay calls to run in
> > > parallel.  With that code in place, a test boot of the same machine took
> > > 61 seconds to bring the cups up.  I am not sure how we beat the lpj=
> > > case, but it did outperform.
> > >
> > > One thing to note is the total BogoMIPS value is also consistently higher.
> > > I am wondering if this is an effect with the cores being in performance
> > > mode.  I did notice that the parallel calibrate_delay calls did cause the
> > > fans on the machine to ramp up to full speed where the normal sequential
> > > calls did not cause them to budge at all.
> >
> > please check attached patch, that could calibrate correctly.
> >
> > Thanks
> >
> > Yinghai
>
> > [PATCH -v2] x86: Make calibrate_delay run in parallel.
> >
> > On a 4096 cpu machine, we noticed that 318 seconds were taken for bringing
> > up the cpus. By specifying lpj=<value>, we reduced that to 75 seconds.
> > Andi Kleen suggested we rework the calibrate_delay calls to run in
> > parallel.
>
> The risk wit tat suggestion is that it will spectacularly miscalibrate on
> hyperthreading systems.

s/wit tat/with that

Thanks,

Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2011-03-31 09:01    [from the cache]
©2003-2011 Jasper Spaans