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Re: [Qemu-devel] Reporting Heisenbugs in qemu
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] Reporting Heisenbugs in qemu |
Date: |
Wed, 8 May 2013 06:18:40 -0400 (EDT) |
> Paolo Bonzini <address@hidden> writes:
>
> I guess that's the register windows. There's only so much you can do to
> optimize them, and heavily recursive workloads (like Perl, or the RTL
> half of GCC) pay a hefty price.
>
> Two qemu targets stand out for slowness, sparc (32 and 64) and mips (64,
> don't know about 32).
>
> x86 (32 and 64), arm, and ppc run with a slowdown of < 30 for my bogus
> benchmark of GMP configure+make.
>
> With FreeBSD x86_64 I see a slowdown of just 13. (My reference system
> runs FreeBSD, so running FreeBSD under qemu is only far.)
>
> My claimed slowdown factors are affected by kernel, libraries, and
> unfortunately very much by gcc speed, which vary with target.
>
> If the sparc emulation speed is due to register windows, then why does
> mips seem just as slow?
No idea. :) Of all the architectures you listed, MIPS is really the one
that I have no inkling of...
> If register windows shortage is a problem, it should be easy to pretend
> to have lots of them, right?
That can help to avoid trapping to the kernel. But you still have to
spill the whole window to the stack on every call to a non-leaf function,
which can be expensive even if you do it in the translated code.
Paolo
- Re: [Qemu-devel] Reporting Heisenbugs in qemu, (continued)
- Re: [Qemu-devel] Reporting Heisenbugs in qemu, Mark Cave-Ayland, 2013/05/07
- Re: [Qemu-devel] Reporting Heisenbugs in qemu, Aurelien Jarno, 2013/05/07
- Re: [Qemu-devel] Reporting Heisenbugs in qemu, Artyom Tarasenko, 2013/05/07
- Re: [Qemu-devel] Reporting Heisenbugs in qemu, Aurelien Jarno, 2013/05/07
- Re: [Qemu-devel] Reporting Heisenbugs in qemu, Aurelien Jarno, 2013/05/08
- Re: [Qemu-devel] Reporting Heisenbugs in qemu, Rob Landley, 2013/05/08