Re: [Qemu-devel] [PATCH v3 00/11] Reduce lock contention on TCG hot-path

[Paolo Bonzini]

On 12/07/2016 22:13, Sergey Fedorov wrote:
> From: Sergey Fedorov <address@hidden>
> 
> Hi,
> 
> This is my respin of Alex's v2 series [1].
> 
> The first 8 patches are preparation for the patch 9, the subject matter
> of this series, which enables lockless translation block lookup. The
> main change here is that Paolo's suggestion is implemented: TBs are
> marked with invalid CPU state early during invalidation. This allows to
> make lockless lookup safe from races on 'tb_jmp_cache' and direct block
> chaining.

Thanks for looking at the suggestion again and especially for perfecting it!

> The patch 10 is a simple solution to avoid unnecessary bouncing on
> 'tb_lock' between tb_gen_code() and tb_add_jump(). A local variable is
> used to keep track of whether 'tb_lock' has already been taken.
> 
> The last patch is my attempt to restructure tb_find_{fast,slow}() into a
> single function tb_find(). I think it will be easier to follow the
> locking scheme this way. However, I am afraid this last patch can be
> controversial, so it can be simply dropped.

Actually I agree entirely with it.

If anything, for historical reasons one might rename tb_find_physical to
tb_find_slow and leave the tb_find_fast name, but I think the patch is
good as is.

Have you measured performance with the series?  In any case, it's nice
to see MTTCG finally taking shape!

Paolo