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

[David Vrabel]

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.

David
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/