Re: [Qemu-devel] [PATCH] mainloop.c: Keep unlocking BQL during busy-wait spin-out

[Peter Crosthwaite]

Hi Peter,

On Fri, Apr 19, 2013 at 12:22 AM, Peter Lieven <address@hidden> wrote:
> On 15.04.2013 15:08, Anthony Liguori wrote:
>>
>> Peter Crosthwaite <address@hidden> writes:
>>
>>> Modify Anthony's starvation detection logic to keep the BQL unlocked
>>> until the starvation condition goes away. Otherwise the counter has to
>>> count up to 1000 for each needed iteration until the busy-wait is
>>> lifted.
>>>
>>> Reset the counter back to zero once glib_pollfds_fill returns with a
>>> non-zero timout, (indicating a return to normality). The 1000 iteration
>>> wait now only happens once on the transition from normal operation to
>>> busy-wait starvation.
>>>
>>> Anthony's original patch fixed the serial paste bug, but this patch is
>>> also needed to restore performance.
>>>
>>> Signed-off-by: Peter Crosthwaite <address@hidden>
>>
>> I'm going through patches for 1.5 candidates.
>>
>> I believe the paste performance issue has been resolved now and this
>> patch is no longer needed.  I can't find a definitive statement on the
>> list for that though.
>
>
> I am also hitting a problem that occured first after Anthonys original
> patch.
> In my testing environment I had 3 vServers that indepently of the load
> became
> heavily unresponsive after reporting "main-loop: WARNING: I/O thread spun
> for 1000 iterations".
> Even QMP is not responsing from time to time. But I am not using serial.
> From the load statistics
> it seems that the vServers is using one complete core busy waiting.
>
> I haven't seen this before this patch.

Are you referring to my patch or Anthonys patch here? Does this patch
introduce a regression (or even a change in behaviour) for you?

Regards,
Peter

>
> Peter
>
>