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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~

  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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