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Re: [Qemu-devel] [PATCH v2 0/3] io-thread optimizations

From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH v2 0/3] io-thread optimizations
Date: Tue, 26 Apr 2011 09:36:30 +0200
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On 2011-04-25 20:35, Aurelien Jarno wrote:
> On Thu, Apr 14, 2011 at 09:14:35AM +0200, Jan Kiszka wrote:
>> On 2011-04-13 22:16, Aurelien Jarno wrote:
>>> On Mon, Apr 11, 2011 at 10:27:41PM +0200, Jan Kiszka wrote:
>>>> These patches were posted before. They bring down the overhead of the
>>>> io-thread mode for TCG here, specifically when emulating SMP.
>>>> The major change in this version, besides rebasing, is the exclusion of
>>>> KVM from the main loop polling optimization.
>>>> Jan Kiszka (3):
>>>>   Do not drop global mutex for polled main loop runs
>>>>   Poll main loop after I/O events were received
>>>>   Do not kick vcpus in TCG mode
>>>>  cpus.c   |    2 +-
>>>>  sysemu.h |    2 +-
>>>>  vl.c     |   22 ++++++++++++++++------
>>>>  3 files changed, 18 insertions(+), 8 deletions(-)
>>> Thanks for working on improving the io-thread with TCG. Your patches 
>>> make sense, but they don't seems to fix the slowdown observed when
>>> enabling the io-thread. Well maybe they were not supposed to. This is
>>> for example the results of netperf between guest and host using virtio:
>>> no io-thread            122 MB/s
>>> io-thread                97 MB/s
>>> io-thread + patches      98 MB/s
>> Can you capture ftraces of io-thread enabled & disabled runs? They just
>> need to cover a hand full of frames.
> From what I have been able to get from the ftraces documentation, it's
> possible multiple tracers. Which tracers would you like to use there?
> The best would be a set of command lines to run.

Sorry, of course: Just download, build & install trace-cmd [1], then
execute "trace-cmd record -b 16000 -e all" while qemu is running. The
result is written to trace.dat in the current directory. Visualize it
via "trace-cmd report" (or kernelshark if you built that as well).


[1] git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/trace-cmd.git

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