Subject: Re: [PATCH v6 2/5] cpufreq: powernv: Remove cpu_to_chip_id() from hot-path

From: Gautham R Shenoy <[email-masked]>
Date: Mon, 25 Jan 2016 11:08:05 +0530

Hello Balbir,

On Sat, Jan 23, 2016 at 07:59:20PM +1100, Balbir Singh wrote:
> On Fri, 22 Jan 2016 12:49:02 +0530
> Shilpasri G Bhat <[email-masked]> wrote:
> 
> > cpu_to_chip_id() does a DT walk through to find out the chip id by
> > taking a contended device tree lock. This adds an unnecessary overhead
> > in a hot path. So instead of calling cpu_to_chip_id() everytime cache
> > the chip ids for all cores in the array 'core_to_chip_map' and use it
> > in the hotpath.
> > 
> > Reported-by: Anton Blanchard <[email-masked]>
> > Signed-off-by: Shilpasri G Bhat <[email-masked]>
> > Reviewed-by: Gautham R. Shenoy <[email-masked]>
> 
> snip
> 
> Does the core_to_chip_map need to be updated/refreshed on/after/ a
> cpu (core) hotplug? I presume id's don't change

No, the id's don't change on cpu/core hotplug. The core_to_chip_map is
initialized in init_chip_info() where we use for_each_possible_cpu().

Thanks for the review!
> Balbir
--
Thanks and Regards
gautham.