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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Thu, 14 Jul 2016 13:02:01 +0100
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Subject: Re: [Qemu-devel] [PATCH v3 00/11] Reduce lock contention on TCG
 hot-path
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sergey Fedorov <sergey.fedorov@linaro.org>, qemu-devel@nongnu.org, mttcg@listserver.greensocs.com, fred.konrad@greensocs.com, a.rigo@virtualopensystems.com, serge.fdrv@gmail.com, cota@braap.org, bobby.prani@gmail.com, rth@twiddle.net, peter.maydell@linaro.org, patches@linaro.org, claudio.fontana@huawei.com, mark.burton@greensocs.com, jan.kiszka@siemens.com


Paolo Bonzini <pbonzini@redhat.com> writes:

> On 12/07/2016 22:13, Sergey Fedorov wrote:
>> From: Sergey Fedorov <serge.fdrv@gmail.com>
<snip>
>
> Have you measured performance with the series?  In any case, it's nice
> to see MTTCG finally taking shape!

Here are some numbers on the multi-threaded pigz test:

Before:

retry.py called with ['./arm-linux-user/qemu-arm', './pigz.armhf', '-c', '-9', 'linux-4.6.3.tar']
Source code is @ pull-tcg-20160708-104-g9ec3025 or heads/review/hot-patch-v3
run 1: ret=0 (PASS), time=32.285497 (1/1)
run 2: ret=0 (PASS), time=32.035293 (2/2)
run 3: ret=0 (PASS), time=31.784781 (3/3)
run 4: ret=0 (PASS), time=32.035136 (4/4)
run 5: ret=0 (PASS), time=32.285612 (5/5)
Results summary:
0: 5 times (100.00%), avg time 32.085 (0.04 varience/0.21 deviation)

After:

Ran command 5 times, 5 passes
retry.py called with ['./arm-linux-user/qemu-arm', './pigz.armhf', '-c', '-9', 'linux-4.6.3.tar']
Source code is @ pull-tcg-20160708-115-gf317fa8 or heads/review/hot-patch-v3
run 1: ret=0 (PASS), time=29.281950 (1/1)
run 2: ret=0 (PASS), time=29.285588 (2/2)
run 3: ret=0 (PASS), time=29.282065 (3/3)
run 4: ret=0 (PASS), time=29.282397 (4/4)
run 5: ret=0 (PASS), time=29.282045 (5/5)
Results summary:
0: 5 times (100.00%), avg time 29.283 (0.00 varience/0.00 deviation)
Ran command 5 times, 5 passes

Which gives a roughly 10% improvement for heavily threaded code.

Looking at the perf data it looks like the hotest part of the code now
is cpu_get_tb_cpu_state which is required to get the initial hash to
search for the next tb.

--
Alex Bennée