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

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

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

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...

Ross Lagerwall

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