Re: [Qemu-devel] [RFC v3] translate-all: protect code_gen_buffer with RCU

["Alex Bennée" <alex.bennee@linaro.org>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 30/04/2016 05:40, Emilio G. Cota wrote:
>>> The tb_flush
>>> > is a fairly rare occurrence its not like its on the critical performance
>>> > path (although of course pathological cases are possible).
>> This is what I thought from the beginning, but wanted to give this
>> alternative a go anyway to see if it was feasible.
>>
>> On my end I won't do any more work on this approach. Will go back
>> to locks, despite Paolo's (justified) dislike for them =)
>
> Which locks?  tb_lock during tb_find_fast?  The problem with that was
> that it slowed down everything a lot, wasn't it?

Very much so, in the new tree (coming soon) with QHT I was able to
remove the locks from the whole hot-path which means they where only
needed for code generation.

> To me, the RCU idea is not really about making tb_flush (the rare case)
> faster; it was more about keeping the rest simple and fast.

I'm not sure it achieved that as there is added complexity from having
the split buffer and then ensuring you don't double-flush.

>
> Paolo


--
Alex Bennée