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

[Steven Rostedt]

On Wed, 2013-06-26 at 08:21 -0700, 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?

I thought the whole deal with this patchset was to remove stop_machine
from CPU hotplug. Why halt all CPUs just to remove one? stomp_machine()
is extremely intrusive for the entire system, where as one CPU making
sure all CPUs schedule isn't very intrusive at all.

I didn't think the idea of this patch set was to make CPU hotplug
faster, just less intrusive to the system.

-- Steve


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