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Re: [Qemu-devel] [patch] performance improvement (softmmu, x86, GCC 3)

From: André Braga
Subject: Re: [Qemu-devel] [patch] performance improvement (softmmu, x86, GCC 3)
Date: Sat, 31 Jul 2004 02:00:48 -0300

Awesome ;)

I haven't dug into the code, so could you please tell me if the ecx
thing you mentioned in the bottom of your message and disabling GCSE
are mutually exclusive? Have you tried to narrow the problem down to
one or more of the separate GCSE flags, instead of the broader
-f[no-]gcse one?

"A year spent in artificial intelligence is enough to make one believe in God"
Alan J. Perlis

On Wed, 28 Jul 2004 07:24:42 -0700 (PDT), Piotr Krysik
<address@hidden> wrote:
> Hi!
> I'm attaching a small patch to enable assembly
> implementation of ld, lds and st (from
> softmmu_header.h) for GCC 3.3 and GCC 3.4 when
> running softmmu x86 guest on x86 host.
> With my simple benchmark (dd if=/dev/zero bs=1M
> count=16 | gzip -9 on Linux guest) this patch
> improves performance by about 8% (QEMU compiled
> with GCC 3.3 on Pentium II Debian host).
> Regards,
> Piotrek
> PS. I also considered removing "%ecx" from register
> constraints of st (softmmu_header.h, line 224) and
> explicitly saving ecx before calling __st (line 198),
> but performance gain was much smaller. I suspect that
> gcse optimization and asm blocks under GCC 3.3 and
> GCC 3.4 don't mix well in QEMU.

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