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From: Ross Lagerwall <ross.lagerwall@citrix.com>
To: David Vrabel <david.vrabel@citrix.com>, xen-devel@lists.xenproject.org
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH] xen/manage: Always freeze/thaw processes when suspend/resuming
Date: Fri, 22 Aug 2014 15:39:09 +0100	[thread overview]
Message-ID: <53F7560D.50004@citrix.com> (raw)
In-Reply-To: <53F722E9.4060505@citrix.com>

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

      reply	other threads:[~2014-08-22 14:39 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-08-18  9:41 [PATCH] xen/manage: Always freeze/thaw processes when suspend/resuming Ross Lagerwall
2014-08-22 11:00 ` David Vrabel
2014-08-22 14:39   ` Ross Lagerwall [this message]

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