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From: Pranith Kumar <bobby.prani@gmail.com>
Date: Mon, 27 Mar 2017 23:07:14 -0400
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Subject: Re: [Qemu-devel] GSoC 2017 Proposal: TCG performance enhancements
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>, Peter Maydell <peter.maydell@linaro.org>, "Emilio G. Cota" <cota@braap.org>, =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>, qemu-devel <qemu-devel@nongnu.org>

Hi Paolo,

On Mon, Mar 27, 2017 at 7:32 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>
> On 25/03/2017 17:52, Pranith Kumar wrote:
>> * Implement an LRU translation block code cache.
>>
>>   In the current TCG design, when the translation cache fills up, we flush all
>>   the translated blocks (TBs) to free up space. We can improve this situation
>>   by not flushing the TBs that were recently used i.e., by implementing an LRU
>>   policy for freeing the blocks. This should avoid the re-translation overhead
>>   for frequently used blocks and improve performance.
>
> IIRC, Emilio measured one flush every roughly 10 seconds with 128 MB
> cache in system emulation mode---and "never" is a pretty accurate
> estimate for user-mode emulation.  This means that a really hot block
> would be retranslated very quickly.
>

OK. The problem with re-translation is that it is a serializing step
in the current design. All the cores have to wait for the translation
to complete. I think it will be a win if we could avoid it, although,
I should admit that I am not sure how much that benefit would be.

-- 
Pranith