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Re: [Qemu-devel] Improve QEMU performance with LLVM codegen and other te

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] Improve QEMU performance with LLVM codegen and other techniques
Date: Thu, 1 Dec 2011 07:46:57 +0000
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, Dec 01, 2011 at 11:50:24AM +0800, 陳韋任 wrote:
> > I don't see any better approach to debugging this than the one you're 
> > already taking. Try to run as many workloads as you can and see if they 
> > break :). Oh and always make the optimization optional, so that you can 
> > narrow it down to it and know you didn't hit a generic QEMU bug.
>   You mean make the trace optimization optional? We have tested our framework 
> in
> LLVM-only mode. which means we replace TCG with LLVM entirely. It's _very_ 
> slow
> but works.

It would be interesting to use an optimized interpreter instead of TCG,
then go to LLVM for hot traces.  This is more HotSpot-like with the idea
being that the interpreter runs through initialization and rarely
executed code without a translation overhead.  For the hot paths LLVM
kicks in and high-quality translated code is executed.


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