Re: [Qemu-devel] [patch 0/3] kvmclock: Ensure time in migration never goes backward (v3)

[Andrey Korolyov]

On Sat, Sep 6, 2014 at 3:05 AM, Andrey Korolyov <address@hidden> wrote:
> On Sat, Sep 6, 2014 at 2:14 AM, Paolo Bonzini <address@hidden> wrote:
>> Il 05/09/2014 21:35, Andrey Korolyov ha scritto:
>>> - boot up a VM, make sure to feed it heavy long task, for example
>>> kernel compilation,
>>> - neither migrate once in the middle of process (with fallback to
>>> non-live migration which is available in libvirt, else it may take
>>> forever) or just wait up to the end,
>>> - live migration time degrades from sub-10s value to larger values
>>> forever, not regarding if workload is still presented or not.
>>
>> Are you sure you aren't simply doing migration with a low bandwidth
>> limit (the default is 32 MB/s), and moving over a gigabyte worth of page
>> cache data to the new machine?
>>
>> Paolo
>
> As far as I can see setspeed does not change anything over stdev
> variation for gigabit, but rss size does. Will check if this part is
> actually broken, because we are overriding default speed value every
> time and if it started being constant, it may explain such a
> difference.

The mess was caused by libvirt which sets migration bandwidth to 8
EB/s, so process took shorter times when I expect from it to utilize
some percent of server interconnection bandwidth.