Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump()

[Sergey Fedorov]

On 08/07/16 11:40, Paolo Bonzini wrote:
> Even better: add a "bool *tb_locked" argument to tb_find_slow, and
> don't move the mmap_lock release.  Then tb_find_fast knows directly
> whether tb_lock is taken, and you don't need any of tb_lock_reset
> or mmap_lock_reset.

I think we can do even better. One option is using a separate tiny lock
to protect direct jump set/reset instead of tb_lock.

Another option which I've had in my mind for some time is to make direct
jump set/reset thread-safe. We already have thread-safe TB patching. The
only question is the right order of operations and handling
jmp_list_next/jmp_list_first safely. I think that could be done by
removing tb_remove_from_jmp_list() and making RCU-like manipulation with
jmp_list_next/jmp_list_first. What do you think?

Kind regards,
Sergey