From: Richard Henderson <rth@twiddle.net>
To: Alexander Graf <agraf@suse.de>
Cc: qemu-devel@nongnu.org, aurelien@aurel32.net
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 [thread overview]
Message-ID: <4C0D4C5E.8030708@twiddle.net> (raw)
In-Reply-To: <7222640D-96FF-41DA-A41D-6D2CB6D669DB@suse.de>
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~
next prev parent reply other threads:[~2010-06-07 19:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-03 0:26 [Qemu-devel] [PATCH 0/2] tcg cleanups, part 4 Richard Henderson
2010-06-03 0:26 ` [Qemu-devel] [PATCH 1/2] tcg: Add TYPE parameter to tcg_out_mov Richard Henderson
2010-06-04 19:19 ` Blue Swirl
2010-06-04 19:34 ` Richard Henderson
2010-06-03 0:26 ` [Qemu-devel] [PATCH 2/2] tcg: Make some tcg-target.c routines static Richard Henderson
2010-06-03 9:23 ` [Qemu-devel] [PATCH 0/2] tcg cleanups, part 4 malc
2010-06-04 0:35 ` [Qemu-devel] [PATCH 0/2] tcg-i386: merge 64-bit, guest_base improvement Richard Henderson
2010-06-04 0:35 ` [Qemu-devel] [PATCH 1/2] tcg-i386: Merge 64-bit generation Richard Henderson
2010-06-09 22:18 ` Aurelien Jarno
2010-06-04 0:35 ` [Qemu-devel] [PATCH 2/2] tcg-i386: Use segment registers to implement GUEST_BASE Richard Henderson
2010-06-04 6:35 ` Alexander Graf
2010-06-07 19:45 ` Richard Henderson [this message]
2010-06-09 9:42 ` [Qemu-devel] [PATCH 0/2] tcg cleanups, part 4 Aurelien Jarno
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