Subject: Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus_atomic() to prevent CPU offline

From: "Srivatsa S. Bhat" <[email-masked]>
Date: Wed, 26 Jun 2013 23:52:17 +0530

On 06/26/2013 08:51 PM, Tejun Heo wrote:
> On Wed, Jun 26, 2013 at 10:51:11AM -0400, Steven Rostedt wrote:
>>> It would also increase the latency of CPU-hotunplug operations.
>>
>> Is that a big deal?
> 
> I thought that was the whole deal with this patchset - making cpu
> hotunplugs lighter and faster mostly for powersaving.  That said, just
> removing stop_machine call would be a pretty good deal and I don't
> know how meaningful reducing CPU hotunplug latency is.  Srivatsa?
> 

Keeping the hotunplug latency is important for suspend/resume, where
we take all non-boot CPUs in a loop. That's an interesting use-case
where intrusiveness doesn't matter much, but latency does. So yes,
making CPU hotplug faster is also one of the goals of this patchset.

Regards,
Srivatsa S. Bhat