On Thu, 2011-02-17 at 07:56 +0000, Shriram Rajagopalan wrote:
> Add documentation to pm.h on how xen uses PM events (freeze,
> thaw, restore) to implement Guest VM save/checkpoint/restore
> functionality.
The change to freeze/thaw/restore instead of suspend/resume raises the
question of what the correct .config option for Xen to key off is.
Currently the Xen suspend functionality in drivers/xen/manage.c is keyed
off CONFIG_PM_SLEEP (which depends on SUSPEND || HIBERNATION ||
XEN_SAVE_RESTORE).
Since PMSG_{SUSPEND,RESUME} are covered by CONFIG_SUSPEND in pm_op()
this already seems incorrect before this change, since PM_SLEEP can be
enabled without SUSPEND, and is equally incorrect after changing to
PMSG_{FREEZE,THAW,RESUME}, which are covered by CONFIG_HIBERNATION.
Is the correct fix to update pm_op to include
|| defined(CONFIG_XEN_SAVE_RESTORE)
where appropriate in pm_op()?
Or should we be looking to adjust the Kconfig and/or code on the Xen
side? Having Xen depend on HIBERNATION ="Hibernation (aka 'suspend to
disk')" seems semantically incorrect.
Ian.
>
> Signed-off-by: Shriram Rajagopalan <rshriram@xxxxxxxxx>
> ---
> include/linux/pm.h | 19 +++++++++++++++++++
> 1 files changed, 19 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/pm.h b/include/linux/pm.h
> index dd9c7ab..2ddd9d3 100644
> --- a/include/linux/pm.h
> +++ b/include/linux/pm.h
> @@ -516,6 +516,25 @@ extern void update_pm_runtime_accounting(struct device *dev);
> * well as during system sleep states like PM_SUSPEND_STANDBY. They may
> * be able to use wakeup events to exit from runtime low-power states,
> * or from system low-power states such as standby or suspend-to-RAM.
> + *
> + * Xen Guest Kernels use PM_FREEZE, PM_RESTORE and PM_THAW to implement
> + * VM save/restore/checkpoint functionality. Save and Restore are somewhat
> + * similar to hibernate functionality. The sequence of events is shown below:
> + * dpm_suspend_start(PMSG_FREEZE);
> + *
> + * dpm_suspend_noirq(PMSG_FREEZE);
> + *
> + * sysdev_suspend(PMSG_FREEZE);
> + * cancelled = suspend_hypercall()
> + * sysdev_resume();
> + *
> + * dpm_resume_noirq(cancelled ? PMSG_THAW : PMSG_RESTORE);
> + *
> + * dpm_resume_end(cancelled ? PMSG_THAW : PMSG_RESTORE);
> + *
> + * If the syspend_hypercall returns 1, it means that the VM was merely
> + * checkpointed (akin to THAW). If it returns 0, it means the system has been
> + * fully restored from its on-disk snapshot (akin to RESTORE).
> */
>
> #ifdef CONFIG_PM_SLEEP
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