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Date: Mon, 17 Aug 2015 23:08:37 +0200
From: Aurelien Jarno <aurelien@aurel32.net>
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Subject: Re: [Qemu-devel] Debian 7.8.0 SPARC64 on qemu - anything i can do
 to speedup the emulation?
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To: Artyom Tarasenko <atar4qemu@gmail.com>
Cc: Karel Gardas <gardask@gmail.com>, alex.bennee@linaro.org, qemu-devel <qemu-devel@nongnu.org>, Dennis Luehring <dl.soluz@gmx.net>, Richard Henderson <rth@twiddle.net>

On 2015-08-17 18:25, Artyom Tarasenko wrote:
> On Mon, Aug 17, 2015 at 5:40 PM, Richard Henderson <rth@twiddle.net> wrote:
> > On 08/17/2015 07:19 AM, Artyom Tarasenko wrote:
> >> Well, on the other hand, every access goes via helper_check_align.
> >> There is a comment /* XXX remove alignment check */.
> >> I wonder how this can be done in a  more efficient way?
> >
> > Not ever access does so.  There are only 3 memory related calls to check_align.
> >  The other three are for indirect branches.
> 
> Yes, but I think it's the 3 most used ones.
> 
> > For the 8 byte memory operations we can just remove the checks.  There, the
> > softmmu operation checks the alignment.
> 
> This is a good news. Where does it happen?
> 
> > For usermode, we've typically ignored
> > the guest alignment (which also causes failures for a host that requires
> > alignment emulating a guest that does not).

A tiny bit of topic, but couldn't we force the use of unaligned access 
load/store instructions in user mode instead? For example in QEMU we
can use the LWL/LWR couple instead of LW. I doubt it will make any
measurable difference in speed. For the MIPS case, that doesn't work
for 16-bit load/stores though.

The best would indeed be to switch to softmmu for the user mode. I know
there are people working on that, but given that it might take time, it
could be a simple temporary solution.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net