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Re: [Xen-devel] [PATCH 1/4] xen: disable non-boot VCPUs during suspend

On 20/06/13 11:38, Jan Beulich wrote:
>>>> On 19.06.13 at 17:25, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>> syscore_suspend() and syscore_resume() expect there to be only one
>> online CPU.  e.g., hrtimers_resume() only triggers events for the
>> current CPU.  Xen's suspend path was leaving all VCPUs online and then
>> attempting to fixup problems afterwards (e.g., with an explicit call
>> to clock_was_set() to trigger pending high resolution timers).
>> Instead, disable non-boot CPUs before calling stop_machine() and
>> reenable them afterwards.
> In XenoLinux the so called "fast suspend" mode was specifically
> added for performance reasons, and it looks like to date pv-ops
> only ever supported that mode. So one question is whether
> there's going to be any bad performance effect from this.

Yes :(

On a VM with 4 VCPUs, disable_boot_cpus() took > 200 ms.

I'll have to rethink this.


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