Re: [Qemu-devel] GSoC 2017 Proposal: TCG performance enhancements

[Paolo Bonzini]

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.

Paolo