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Re: [Qemu-devel] Re: branches are expensive
From: |
Paul Brook |
Subject: |
Re: [Qemu-devel] Re: branches are expensive |
Date: |
Thu, 19 Mar 2009 11:34:49 +0000 |
User-agent: |
KMail/1.9.9 |
> I've tested Qemu 0.10.0 and with i386-softmmu on a i386 host I get the
> following numbers:
> direct jump count 70%, 2 jumps 54%
>
> For completeness I tested qemu-system-arm on a i386 host as well:
> direct jump count 44%, 2 jumps 37%
>
> So it looks like the chaining on ARM targets is not as effective as on i386
> targets (regardless of the guest, I used the same guest setup, compiled for
> different architectures, on all tests). Do you have any ideas why this is
> the case?
A couple of likely reasons:
- ARM uses 1k pages, i386 uses 4k pages, so there's greater probability of
spanning a page boundary.
- ARM has conditional execution, so code will tend to have less conditional
branches. The number of function calls (in particular function returns, which
are indirect branches) is likely to be about the same, so the proportion of
direct jumps is less.
Paul
- Re: [Qemu-devel] branches are expensive, (continued)
- Re: [Qemu-devel] branches are expensive, Avi Kivity, 2009/03/17
- [Qemu-devel] Re: branches are expensive, Jan Kiszka, 2009/03/17
- [Qemu-devel] Re: branches are expensive, Steffen Liebergeld, 2009/03/17
- Re: [Qemu-devel] Re: branches are expensive, Paul Brook, 2009/03/17
- Re: [Qemu-devel] Re: branches are expensive, Avi Kivity, 2009/03/17
- [Qemu-devel] Re: branches are expensive, Steffen Liebergeld, 2009/03/19
- Re: [Qemu-devel] Re: branches are expensive, Laurent Desnogues, 2009/03/19
- [Qemu-devel] Re: branches are expensive, Steffen Liebergeld, 2009/03/19
- Re: [Qemu-devel] Re: branches are expensive, Laurent Desnogues, 2009/03/19
- Re: [Qemu-devel] Re: branches are expensive, Avi Kivity, 2009/03/19
- Re: [Qemu-devel] Re: branches are expensive,
Paul Brook <=
[Qemu-devel] Re: branches are expensive, Steffen Liebergeld, 2009/03/17
Re: [Qemu-devel] branches are expensive, Laurent Desnogues, 2009/03/17