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Re: [Qemu-devel] Storing code caching

From: John R. Hogerhuis
Subject: Re: [Qemu-devel] Storing code caching
Date: Thu, 08 Jul 2004 12:45:12 -0700

On Thu, 2004-07-08 at 12:11, Julian Seward wrote:

> Nice idea, but ... I suspect it solves a non-problem really.  Caching
> translations is only worthwhile when translation time is a large
> part of overall run time, but I bet that's not the case.  It certainly
> isn't with Valgrind, which uses similar technology.

Right. That's entirely possible, but just as much speculation without
any numbers.

No one knows until the work or analysis is done...

Translation time is certainly not negligible. And a better code
generator would quite likely swamp any improvements a persistent cache
could give. There's disk I/O to consider there too. But it is possible
the improvements would make a faster emulator.

It depends on requirements too I guess. If you don't care about load
time then you probably don't care about translation time either since
from the user's point of view they are going to be conflated.

> If you want to throw lots of hacking effort at QEMU to make it
> go faster, I suspect you'll need to be building a more sophisticated
> code generator, a la "lcc" (http://www.cs.princeton.edu/software/lcc).

Interesting... why do you bring up lcc specifically? Just browsing that
page and its FAQ didn't tell me much about it other than it is a
retargetable C compiler.

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