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SubjectRe: [PATCH 2/6] powerpc, powernv, CPU hotplug: Put offline CPUs in Fast-Sleep instead of Nap
On Wed, May 28, 2014 at 10:08:56AM +0530, Preeti U Murthy wrote:
> From: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
>
> The offline cpus are put to fast sleep if the idle state is discovered in the
> device tree. This is to gain maximum powersavings in the offline state.

...

> while (!generic_check_cpu_restart(cpu)) {
> ppc64_runlatch_off();
> - power7_nap();
> +
> + /* If sleep is supported, go to sleep, instead of nap */
> + if (idle_states & IDLE_USE_SLEEP)
> + power7_sleep();
> + else
> + power7_nap();
> +
> ppc64_runlatch_on();
> if (!generic_check_cpu_restart(cpu)) {
> DBG("CPU%d Unexpected exit while offline !\n", cpu);

What is the latency for waking up from fast sleep state? I'm concerned
this will increase the latency for entering KVM guests.

Paul.


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