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Re: [libvirt] [PATCH v3 0/2] API to invoke S3/S4 on a host and also resume from within libvirt



On 11/22/2011 05:56 AM, Eric Blake wrote:
> On 11/09/2011 05:05 AM, Srivatsa S. Bhat wrote:
>> (This patch is positioned to go in after the patch that exports the host
>> power management capabilities as XML, posted in [4])
> 
> I'm now reviewing that patch along with this series; if we need another
> revision, it may be easiest to merge the three patches into a single
> series and title it v6, so that they are together in one thread.
> 
>>
>> This patch adds a new API to put a host to a suspended state (either
>> Suspend-to-RAM or Suspend-to-Disk) and setup a timed resume to get the
>> host back online, from within libvirt.
>> This uses the RTC wakeup mechanism to set up a timer alarm before
>> suspending the host, so that in-band resume is facilitated by the firing
>> of the RTC alarm, which wakes up the host.
> 
> I'm not as familiar with S3/S4 as I would like to be - am I correct that
> RTC wakeup works for S3 (where the host is maintaining minimal power and
> can thus react to interrupts), but not S4 (where the host has flushed
> completely to disk and powers off, but resumes from the state on disk on
> next power on)?  Or am I misunderstanding these two power-saving states?
>

Actually, RTC wakeup works for both S3 and S4. Hence this patch can use
that mechanism effectively for both the system-wide sleep states.

Thanks,
Srivatsa S. Bhat
IBM Linux Technology Center


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