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[Qemu-devel] Re: [PATCH] qemu/pci: optimize pci config handling
From: |
Michael S. Tsirkin |
Subject: |
[Qemu-devel] Re: [PATCH] qemu/pci: optimize pci config handling |
Date: |
Wed, 7 Oct 2009 21:21:27 +0200 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
On Wed, Oct 07, 2009 at 04:24:45PM +0200, Paolo Bonzini wrote:
>> I'm actively trying to get out of range-checking address.
>
> I don't understand what you mean, sorry.
>
>> What you porpose here is certainly more code than we had.
>> So why is this a good idea?
>
> Because it avoids the memcpy/memcmp most of the time (when the memcmp
> would surely succeed).
Yes :) But at the cost of more code. I don't think speed
matters there, so less code is good. But even if it did, extra
read of a single cache line might be cheaper than an extra branch,
and generated code will be more compact.
> I supposed that would also matter more as the
> config space size increases---correct me and dismiss the patch if I am
> mistaken.
No, we'll always only look need to look at the header, whatever the size
of the config space. That's the point of the patch I posted - future
proof against config space size increases, not optimization.
> Paolo
[Qemu-devel] Re: [PATCH] qemu/pci: optimize pci config handling, Isaku Yamahata, 2009/10/07