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

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.