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Date: Mon, 25 Jan 2016 11:08:05 +0530
From: Gautham R Shenoy <ego@linux.vnet.ibm.com>
To: Balbir Singh <bsingharora@gmail.com>
Cc: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>, linuxppc-dev@ozlabs.org,
 linux-kernel@vger.kernel.org, rjw@rjwysocki.net,
 viresh.kumar@linaro.org, linux-pm@vger.kernel.org, pc@us.ibm.com,
 anton@samba.org, ego@linux.vnet.ibm.com, shreyas@linux.vnet.ibm.com
Subject: Re: [PATCH v6 2/5] cpufreq: powernv: Remove cpu_to_chip_id() from
 hot-path
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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 <shilpa.bhat@linux.vnet.ibm.com> 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 <anton@samba.org>
> > Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
> > Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> 
> 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.