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Re: [Qemu-devel] qemu vs gcc4
From: |
Paul Brook |
Subject: |
Re: [Qemu-devel] qemu vs gcc4 |
Date: |
Tue, 31 Oct 2006 23:00:42 +0000 |
User-agent: |
KMail/1.9.5 |
On Tuesday 31 October 2006 22:31, Laurent Desnogues wrote:
> Paul Brook a écrit :
> > Replacing the pregenerated blocks with hand written assembly isn't
> > feasible. Each target has its own set of ops, and each host would need
> > its own assembly implementation of those ops. Multiply 11 targets by 11
> > hosts and you get a unmaintainable mess :-)
>
> Shouldn't you have 11+11 and not 11*11, given your intermediate
> representation? And of these 11+11, 11 have to be written
> anyway (target). Or did I miss something?
If you use qops (which is a target and host independent intermediate
representation) it's 11 + 11. If you just replace the existing dyngen op.c
with hand written assembly it's 11 * 11.
> > On RISC targets like ARM most instructions don't set the condition codes,
> > so we don't bother doing this.
>
> Except for ARM Thumb ISA which always sets flags. ARM is a bad
> RISC example :)
Bah. Details :-)
> I was wondering if you did some profiling to know how much time
> is spent in disas_arm_insn. Of course the profiling results
> would be very different for a Linux boot or a synthetic benchmark
The qop generator does add some overhead to the code translation. I haven't
done proper benchmarks, but in most cases it doesn't seem to be too bad
(maybe 10%). I'm hoping we can get most of that back.
> (which makes me think that you don't support MMU, do you?).
qemu does implement a MMU.
Currently this still uses the dyngen code, but that's fixable.
> There is a very nice trick to speed up decoding of ARM
> instructions: pick up bits 20-27 and 4-7 and you (almost) get
> one instruction per case entry; of course this means using a
> generator to write the 4096 entries, but the result was good for
> my interpreted ISS, reaching 44 M i/s on an Opteron @2.4GHz
> without any compiler dependent trick (such as gcc jump to labels).
qemu generally gets 100-200MIPS on my 2GHz Opteron.
Paul
- Re: [Qemu-devel] qemu vs gcc4, (continued)
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/23
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/24
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/24
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/25
- Re: [Qemu-devel] qemu vs gcc4, Daniel Jacobowitz, 2006/10/26
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Laurent Desnogues, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4,
Paul Brook <=
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/31
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/29
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/30
- Re: [Qemu-devel] qemu vs gcc4, Rob Landley, 2006/10/30
- Re: [Qemu-devel] qemu vs gcc4, Paul Brook, 2006/10/30