Re: [RFD PATCH 1/4] powerpc: cpu: Reduce the polling interval in__cpu_up()

From: Gautham R Shenoy
Date: Tue Jun 16 2009 - 12:37:49 EST

On Tue, Jun 16, 2009 at 11:06:45AM -0500, Nathan Lynch wrote:
> Please cc linuxppc-dev if you want the powerpc maintainer to pick this
> up.

Will do it. I still need to test this patch across the different
configurations. I posted it here just so that we get a rough idea
regarding what we're looking at.

Thanks for taking a look at this one!
> Gautham R Shenoy <ego@xxxxxxxxxx> writes:
> > The cpu online operation on a powerpc today takes order of 200-220ms. Of
> > this time, approximately 200ms is taken up by __cpu_up(). This is because
> > we poll every 200ms to check if the new cpu has notified it's presence
> > through the cpu_callin_map. We poll every 200ms until the new cpu sets
> > the value in cpu_callin_map or 5 seconds elapse, whichever comes earlier.
> >
> > However, the time taken by the new processor to indicate it's presence has
> > found to be less than a millisecond
> Only with your particular configuration (which is not identified). It
> can take much longer than 1ms on others.
> > Keeping this in mind, reduce the
> > polling interval from 200ms to 1ms while retaining the 5 second
> > timeout.
> Ack on the patch, but the changelog needs work. I assume your
> observations are from a pseries system -- please state this in the
> changelog ("powerpc" is too broad), along with the processor model and
> whether the LPAR's processors were configured in dedicated or shared
> mode.

Will send these details with the patch separately Ccing linux-ppcdev list.

Thanks and Regards
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at