Messages in this thread | | | Date | Tue, 16 Jun 2009 14:00:59 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support. |
| |
On Tue, Jun 16, 2009 at 01:37:15PM +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
Perhaps also reducing boot-up time? If I am correctly interpreting the above numbers, an eight-CPU system would be consuming 175 milliseconds bringing up the seven non-boot CPUs. Reducing this by 150 milliseconds might be of interest to some people. ;-)
Thanx, Paul
> Ref: > > [1] Saving power by cpu evacuation sched_max_capacity_pct=n > http://lkml.org/lkml/2009/5/13/173 > > [2] Make offline cpus to go to deepest idle state using > http://lkml.org/lkml/2009/5/22/431 > > [3] cpuset: add new API to change cpuset top group's cpus > http://lkml.org/lkml/2009/5/19/54 > > For getting stuff off a certain CPU, cpu-hotplug framework seems to do > the right thing. Identifying bottlenecks in the framework can > significantly help other use cases. > > --Vaidy >
| |