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

[Nathan Lynch <ntl@pobox.com>]

Please cc linuxppc-dev if you want the powerpc maintainer to pick this
up.

Gautham R Shenoy <ego@in.ibm.com> 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.