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Re: [Qemu-devel] Translation cache sizes

From: Paul Brook
Subject: Re: [Qemu-devel] Translation cache sizes
Date: Sat, 8 Apr 2006 14:16:43 +0100
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On Saturday 08 April 2006 04:13, Julian Seward wrote:
> 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.
> I made 2 changes:
> * increase CODE_GEN_BUFFER_SIZE from 16*1024*1024
>   to 64*1024*1024,
> * 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.
> 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.

Did you measure any actual speedup from these changes?

In a typical linux boot there's a lot of new code run only once, so I'd expect 
the tb cache to be hammered fairly heavily.


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