Messages in this thread |  | | | Date | Thu, 10 Feb 2011 11:00:51 -0500 (EST) | | From | Alan Stern <> | | Subject | Re: [Xen-devel] Re: [linux-pm] [PATCH 0/2] Fix hangup after creating checkpoint on Xen. |
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On Thu, 10 Feb 2011, Ian Campbell wrote:
> On Wed, 2011-02-09 at 23:42 +0000, Alan Stern wrote: > > In fact there already is a "fast suspend & resume" path in the PM core. > > It's the freeze/thaw procedure used when starting to hibernate. The > > documentation specifically says that drivers' freeze methods are > > supposed to quiesce their devices but not change power levels. In > > addition, the thaw method is invoked as part of recovery from a failed > > hibernation attempt, so it already has the "cancel" semantics that xen > > seems to want. > > Sounds like that would work and I would much prefer to simply make > correct use of the core functionality.
It seems like a reasonable approach. Whether it will actually _work_ is a harder question... :-)
> So PMSG_FREEZE is balanced by either PMSG_RECOVER or PMSG_THAW depending > on whether the suspend was cancelled or not?
Basically yes. It is also "balanced" by PMSG_RESTORE, which is used after a memory image has been restored (although this isn't relevant to your snapshotting). See the comments in include/linux/pm.h.
> So the sequence of events > is something like: > dpm_suspend_start(PMSG_FREEZE); > > dpm_suspend_noirq(PMSG_FREEZE); > > sysdev_suspend(PMSG_QUIESCE);
This should say sysdev_suspend(PMSG_FREEZE).
> cancelled = suspend_hypercall()
At this point swsusp_arch_suspend() is called. If that translates to suspend_hypercall() in your setting, then yes.
> sysdev_resume(); > > dpm_resume_noirq(cancelled ? PMSG_RECOVER : PMSG_THAW); > > dpm_resume_end(cancelled ? PMSG_RECOVER : PMSG_THAW); > ?
Yes.
> (For comparison we currently have: > > > > dpm_suspend_start(PMSG_SUSPEND); > > > > > > > > dpm_suspend_noirq(PMSG_SUSPEND); > > > > > > > > sysdev_suspend(PMSG_SUSPEND); > > > > /* suspend hypercall */ > > > > sysdev_resume(); > > > > > > > > dpm_resume_noirq(PMSG_RESUME); > > > > > > > > dpm_resume_end(PMSG_RESUME); > )
Right. The sequence of calls is the same, but the PMSG_ argument is different so drivers are expected to act differently in response. Alan Stern
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