Messages in this thread | | | Date | Wed, 17 Jun 2009 17:07:00 +0200 | From | Ingo Molnar <> | Subject | Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support. |
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> On Wed, Jun 17, 2009 at 09:32:57AM +0200, Peter Zijlstra wrote: > > On Tue, 2009-06-16 at 13:37 +0530, Vaidyanathan Srinivasan wrote: > > > * Andrew Morton <akpm@linux-foundation.org> [2009-06-15 23:23:18]: > > > > > > > On Tue, 16 Jun 2009 11:08:39 +0530 Gautham R Shenoy <ego@in.ibm.com> wrote: > > > > > > > > > Currently on a ppc64 box with 16 CPUs, the time taken for > > > > > a individual cpu-hotplug operation is as follows. > > > > > > > > > > # time echo 0 > /sys/devices/system/cpu/cpu2/online > > > > > real 0m0.025s > > > > > user 0m0.000s > > > > > sys 0m0.002s > > > > > > > > > > # time echo 1 > /sys/devices/system/cpu/cpu2/online > > > > > real 0m0.021s > > > > > user 0m0.000s > > > > > sys 0m0.000s > > > > > > > > Surprised. Do people really online and offline CPUs frequently enough > > > > for this to be a problem? > > > > > > Certainly not for hardware faults or hardware replacement, but > > > cpu-hotplug interface is useful for changing system configuration to > > > meet different objectives like > > > > > > * Reduce system capacity to reduce average power and reduce heat > > > > > > * Increasing number of cores and threads in a CPU package is leading > > > to multiple cpu offline/online operations for any perceivable effect > > > > > > * Dynamically change CPU configurations in virtualized environments > > > > I tend to agree with Andrew, if any of those things are done > > frequent enough that the hotplug performance matter you're doing > > something mighty odd. > > Boot speedup?
Also, if it brings more attention (and more stability and more bugfixes) to CPU hotplug that's only good.
Ingo
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