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Re: Change TCG cache size?


From: Alex Bennée
Subject: Re: Change TCG cache size?
Date: Wed, 22 Sep 2021 11:47:21 +0100
User-agent: mu4e 1.7.0; emacs 28.0.50

Kenneth Adam Miller <kennethadammiller@gmail.com> writes:

> Hello all,
>
> I just want to ask this one question: if I change the qemu tcg cache
> size (TB_JMP_CACHE_SIZE), will that force any errors at run time?

Hopefully not - for both user-mode and softmmu we take some care to
ensure tb_jmp_cache_hash_func and tb_jmp_cache_hash_page return
appropriately masked values for the table lookup.

What has not been done since Emilio's work in 6f1653180f (tb-hash:
improve tb_jmp_cache hash function in user mode) is a deeper look at the
hit rate and bounce rate of the softmmu jump table hashing. Any
suggested changes will need some benchmarking to show what difference it
makes.

-- 
Alex Bennée



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