Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2

[Ming Lei]

On Sat, Jun 28, 2014 at 5:51 AM, Paolo Bonzini <address@hidden> wrote:
> Il 27/06/2014 20:01, Ming Lei ha scritto:
>
>> I just implemented plug&unplug based batching, and it is working now.
>> But throughout still has no obvious improvement.
>>
>> Looks loading in IOthread is a bit low, so I am wondering if there is
>> block point caused by Qemu QEMU block layer.
>
>
> What does perf say?  Also, you can try using the QEMU trace subsystem and
> see where the latency goes.

Follows some test result against 8589744aaf07b62 of
upstream qemu, and the test is done on my 2core(4thread)
laptop:

1, with my draft batch patches[1](only linux-aio supported now)
- throughput: +16% compared qemu upstream
- average time spent by handle_notify(): 310us
- average time between two handle_notify(): 1591us
(this time reflects latency of handling host_notifier)

2, same tests on 2.0.0 release(use custom Linux AIO)
- average time spent by handle_notify(): 68us
- average time between calling two handle_notify(): 269us
(this time reflects latency of handling host_notifier)

>From above tests, looks root cause is late handling notify, and
qemu block layer becomes 4times slower than previous custom
linux aio taken by dataplane.

[1], git://kernel.ubuntu.com/ming/qemu.git #master-0626-batch

Thanks,
-- 
Ming Lei