Re: To save or not to save

["Zeeshan Ali (Khattak)" <zeeshanak gnome org>]

On Thu, Nov 15, 2012 at 10:32 PM, Zeeshan Ali (Khattak)
<zeeshanak gnome org> wrote:
> On Thu, Nov 15, 2012 at 9:31 PM, Daniel P. Berrange <berrange redhat com> wrote:
>> On Thu, Nov 15, 2012 at 07:49:46PM +0200, Zeeshan Ali (Khattak) wrote:
>>> Hi everyone,
>>>    As you all know currently we save running local VMs when user quits
>>> Boxes UI. The reason for doing so were:
>>>
>>> 1.  We want to reclaim all the resources (especially RAM, cause CPU
>>> could be saved by only pausing the VM)
>>> 2. VM state should not be lost across reboots/shutdowns of host
>>>
>>> However, saving of VM seems to have been a very heavy operation,
>>> especially on machines with not a lot of RAM (on my machine with only
>>> 4GB RAM, host more or less freezes completely for a few seconds). The
>>> reason AFAICT is that most of guest RAM being unused is swapped out so
>>> saving then involves copying GBs of data per running VM from one part
>>> of the drive to another.
>>
>> Have you tried making Boxes use the
>>
>>   VIR_DOMAIN_SAVE_BYPASS_CACHE
>>
>> flag yet ? oVirt saw serious problems with host performance when
>> saving VMs to disk, unless they used VIR_DOMAIN_SAVE_BYPASS_CACHE
>> to avoid trashing the I/O cache.
>
> Not yet. I somehow forgot about that actually. :( Now added to top of
> my todo file so will do so soon enough. :)

Now I tried many times with and without this flag on my machine. *If*
there is any difference, its that this flag makes the operation
slower: on average I measured a difference of 2 seconds between
hitting 'CTRL+Q" and boxes exiting.

-- 
Regards,

Zeeshan Ali (Khattak)
FSF member#5124