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

[Peter Lieven <lieven-lists@dlhnet.de>]

On 15.04.2013 15:08, Anthony Liguori wrote:
> Peter Crosthwaite <peter.crosthwaite@xilinx.com> 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 <peter.crosthwaite@xilinx.com>
> 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.

Peter