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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 03:48 PM, Alon Levy wrote:
> On Mon, Nov 21, 2011 at 05:26:55PM -0700, 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?
> 
> Theoretically I think you're right, but in current qemu S3 does a
> hardware reset without reseting the memory, so kind of a sleep +
> immediate wakeup. S4 is emulated correctly - qemu doesn't have to do
> anything special.
> 

Hi Alon,
Actually this patchset talks about S3/S4 on the _host_, not the guest.
So, in the host, RTC wakeup works for both S3 and S4.

Thanks,
Srivatsa S. Bhat
IBM Linux Technology Center


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