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Re: [Qemu-devel] Translation cache sizes

From: Mulyadi Santosa
Subject: Re: [Qemu-devel] Translation cache sizes
Date: Sat, 8 Apr 2006 13:30:28 +0700
User-agent: KMail/1.5

Hi Julian...

> Using qemu from cvs simulating x86-softmmu (no kqemu) on x86,
> booting SuSE 9.1 and getting to the xdm (kdm?) graphical login
> screen, requires making about 1088000 translations, and the
> translation cache is flushed 17 times.  Booting is not too bad,
> but once user-mode starts to run the translation cache is pretty
> much hammered.

Reminds me when I booted FC2 default kernel (4G/4G VM split). Maybe I 
suffer the same thing, that is tons of translations and cache flush 
inside qemu.

Anyway, mind to share on how did you get the number? Putting such info 
on qemu forum (http://qemu.dad-answers.com) will be great too since it 
will let/encourage other (casual) user to tweak qemu.

> I made 2 changes:
> * increase CODE_GEN_BUFFER_SIZE from 16*1024*1024
>   to 64*1024*1024,

I think, if speed is what user really need, he/she won't mind with the 
extra 48 MB IMHO. Run qemu in non X environment, use serial output or 
curses based display, the extra 48 MB won't hog too much.

> * observe that CODE_GEN_AVG_BLOCK_SIZE of 128
>   for the softmmu case is too low; my measurements put it
>   at about 247.  So I changed it to 256.

so, you double it....that means, there is more than just the extra 48 

> With those changes in place, the same boot-to-kdm process
> requires only about 570000 translations to be made, and 2
> cache flushes to happen.  Of course the cost is an extra
> 48M of memory use.

Good to hear! Wow! Maybe we should  made those constants configurable 
(using ./configure script)?



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