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Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6
From: |
Ming Lei |
Subject: |
Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2 |
Date: |
Tue, 1 Jul 2014 22:49:22 +0800 |
On Tue, Jul 1, 2014 at 10:31 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Tue, Jul 1, 2014 at 3:53 PM, Ming Lei <address@hidden> wrote:
>> On Mon, Jun 30, 2014 at 4:08 PM, Stefan Hajnoczi <address@hidden> wrote:
>>>
>>> Try:
>>> $ perf record -e syscalls:* --tid <iothread-tid>
>>> ^C
>>> $ perf script # shows the trace log
>>>
>>> The difference between syscalls in QEMU 2.0 and qemu.git/master could
>>> reveal the problem.
>>
>> The difference is that there are tons of write() and rt_sigprocmask()
>> in qemu.git/master, I guess it is related coroutinue.
>>
>> For linux-aio, the coroutinue shouldn't be necessary because
>> io_submit() won't block at most of times for O_DIRECT read/write.
>
> You're forgetting about image formats and the other QEMU block layer
> features like I/O throttling. They do require coroutines.
I mean from linux-aio view, io_submit() won't block most of times, like
your previous implementation of dataplane.
>
> Are you sure it's the extra syscall overhead? Any ideas for avoiding them?
Yes, I am sure, and it can be felt obviously when running perf to
trace system call, :-)
Let me provide some data when running randread(bs 4k, libaio)
from VM for 10sec:
1), qemu.git/master
- write(): 731K
- rt_sigprocmask(): 417K
- read(): 21K
- ppoll(): 10K
- io_submit(): 5K
- io_getevents(): 4K
2), qemu 2.0
- write(): 9K
- read(): 28K
- ppoll(): 16K
- io_submit(): 12K
- io_getevents(): 10K
> The sigprocmask can probably be optimized away since the thread's
> signal mask remains unchanged most of the time.
>
> I'm not sure what is causing the write().
I am investigating it...
Thanks,
--
Ming Lei
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Ming Lei, 2014/07/01
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Stefan Hajnoczi, 2014/07/01
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2,
Ming Lei <=
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Paolo Bonzini, 2014/07/01
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Ming Lei, 2014/07/01
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Stefan Hajnoczi, 2014/07/02
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Paolo Bonzini, 2014/07/02
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Kevin Wolf, 2014/07/02
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Paolo Bonzini, 2014/07/02
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Kevin Wolf, 2014/07/02
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Paolo Bonzini, 2014/07/02
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Ming Lei, 2014/07/02
- Re: [Qemu-devel] [regression] dataplane: throughout -40% by commit 580b6b2aa2, Ming Lei, 2014/07/02