RE: [Xen-devel] Ehancement to domU suspend/resume

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Keir Fraser [mailto:keir@xxxxxxxxxxxxx]
>Sent: 2007年1月18日 15:04
>
>On 18/1/07 2:41 am, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>
>>> freeze_processes();
>>> device_suspend();
>>> device_power_down();
>
>>> device_power_up();
>>> device_resume();
>>> thaw_processes();
>
>Any idea what cost this adds for a non driver domain? In particular, what
>does freeze/thaw do?
>
> -- Keir

Freeze basically puts all other processes into a frozen point with no 
lock held. For kernel thread, each one is required to check freezing 
flag (by try_to_freeze) at each loop out of critical chunk, and then yield 
or sleep if set. For user space process, a dummy signal notification is 
sent to that process which will then check freezing flag when do_signal 
before returning to user space. This can assure all processes falling 
into a save point before drivers are ready to suspend. Thaw just does 
the reverse to unfreeze them when resume.

Yes, it may have to wait some time for all processes to be frozen, and I 
have no estimation. But it's a necessary step to put whole box into a 
stable state. Is there any flag to check whether current domU is a driver 
domain? Then we can differentiate two paths.

Thanks,
Kevin

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