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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 14:10:11 +0100
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On Saturday 08 April 2006 13:43, Gwenole Beauchesne wrote:
> Hi,
> > 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.
> I faced a similar problem in Basilisk II. MacOS 8.x had a tendency to
> invalidate the code cache approx. 1000 times per second. My poor
> K6-2/300 was suffering a lot. About 45% of the time was dedicated to
> compilation of code, and desktop experience was very sluggish. Then, I
> came up with a very simple idea I named "lazy cache flush". Performance
> increased by 76% and compilation time dropped below 10%, desktop
> experience was very smooth. I will give you more contemporary results
> hereunder.

Qemu already does this. Initially it does it on a per-page basis (writes to a 
given physical memory page will invalidate all code on that page), and for 
frequently contested pages it does more fine-grained locking.
x86 doesn't have explicit icache invalidate instructions, the icache is 
architecturally defined to be coherent after every jump instructions.


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