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Re: [Qemu-trivial] [Qemu-devel] [PATCH] tcg: optimise memory layout of T

From: Stefan Weil
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] tcg: optimise memory layout of TCGTemp
Date: Mon, 30 Mar 2015 07:33:59 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.5.0

Am 29.03.2015 um 23:52 schrieb Richard Henderson:
On Mar 27, 2015 14:09, "Emilio G. Cota" <address@hidden> wrote:
On Fri, Mar 27, 2015 at 09:55:03 +0000, Alex Bennée wrote:
Have you been able to measure any performance improvement with these new
structures? In theory, if aligned with cache lines, performance should
improve but real numbers would be nice.
I haven't benchmarked anything, which makes me very uneasy. All
I've checked is that the system boots, and FWIW I appreciate no
difference in boot time.
No decrease in boot time is good. We /know/ we're saving memory, after all.
Is there a benchmark suite to test TCG changes?
No, sorry.


Benchmarking TCG with QEMU's system emulation is nearly impossible
because operating systems usually contain lots of timer based operations.
The TCG interpreter for example is really slow, but a BIOS will boot
faster than expected with it.

The user mode emulation is much better for benchmarks.
Run some command line Linux application which mainly does
computations (not file i/o) using user mode emulation on Linux.
The OpenSSL package contains bntest which can be used
as a benchmark for TCG. Redirect all output to /dev/null when
you run it.

Binaries for i386 and x86_64 are available from


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