Re: [Xen-devel] [PATCH] xen/manage: Always freeze/thaw processes when suspend/resuming

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 08/22/2014 12:00 PM, David Vrabel wrote:
> On 18/08/14 10:41, Ross Lagerwall wrote:
> > Always freeze processes when suspending and thaw processes when resuming
> > to prevent a race noticeable with HVM guests.
> >
> > This prevents a deadlock where the khubd kthread (which is designed to
> > be freezable) acquires a usb device lock and then tries to allocate
> > memory which requires the disk which hasn't been resumed yet.
> > Meanwhile, the xenwatch thread deadlocks waiting for the usb device
> > lock.
> >
> > Freezing processes fixes this because the khubd thread is only thawed
> > after the xenwatch thread finishes resuming all the devices.
> I think this is the safest fix for this issue but I'm a bit concerned
> about how much extra time the freeze_processes() call will add to the
> suspend.
>
> Can you measure how long it takes for a typical VM?
With 2 vCPUs and 1024MB RAM, 8ms for freeze_processes() and 6ms for 
thaw_processes().
With 4 vCPUs and 4096MB RAM, 8ms for freeze_processes() and 5ms for 
thaw_processes().
With 4 vCPUs and 4096MB RAM running stress -c 4, 12ms for 
freeze_processes() and 66ms for thaw_processes().
It doesn't seem to take too long...

Cheers
--
Ross Lagerwall

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