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Re: [Qemu-devel] [PATCH 2/2] tcg-i386: Use segment registers to implemen
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] tcg-i386: Use segment registers to implement GUEST_BASE. |
Date: |
Mon, 07 Jun 2010 12:45:34 -0700 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-3.fc13 Thunderbird/3.0.4 |
On 06/03/2010 11:35 PM, Alexander Graf wrote:
>
> On 04.06.2010, at 02:35, Richard Henderson wrote:
>
>> For 32-bit, using a segment override is smaller than the 4-byte
>> immediate offset. For 64-bit, segments can hold the entire 64-bit
>> offset whereas the 4-byte immediate cannot.
>
> Very nice idea indeed :). Have you found it to be faster? IIRC
> segment accesses are slower when seg_offs != 0. But then again the
> code is smaller, so it might weigh it up.
I've not yet tried to do any proper benchmarking.
I had thought that the segment access was slower only when limit != 4G,
i.e. when the segment boundaries need to be checked. And that 64-bit
segments don't have boundaries, so the slowdown does not apply there either.
I'll put it on my queue for the weekend.
r~
- [Qemu-devel] [PATCH 0/2] tcg cleanups, part 4, Richard Henderson, 2010/06/02
- [Qemu-devel] [PATCH 1/2] tcg: Add TYPE parameter to tcg_out_mov., Richard Henderson, 2010/06/02
- [Qemu-devel] [PATCH 2/2] tcg: Make some tcg-target.c routines static., Richard Henderson, 2010/06/02
- Re: [Qemu-devel] [PATCH 0/2] tcg cleanups, part 4, malc, 2010/06/03
- [Qemu-devel] [PATCH 0/2] tcg-i386: merge 64-bit, guest_base improvement, Richard Henderson, 2010/06/03
- [Qemu-devel] [PATCH 1/2] tcg-i386: Merge 64-bit generation., Richard Henderson, 2010/06/03
- Re: [Qemu-devel] [PATCH 0/2] tcg cleanups, part 4, Aurelien Jarno, 2010/06/09