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Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump() |
Date: |
Fri, 8 Jul 2016 07:02:30 -0400 (EDT) |
> 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.
If you have to use a separate tiny lock, you don't gain anything compared
to the two critical sections, do you?
In any case, this seems to be more complex than necessary. The "bool *"
convention is pretty common in Linux for example---it works well.
The one below is even more complicated. I'm all for simple lock-free
stacks (e.g. QSLIST_INSERT_HEAD_ATOMIC and QSLIST_MOVE_ATOMIC), but lock-free
lists are too much, especially if with the complicated first/next mechanism
of TCG's chained block lists.
Paolo
> 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
>
- Re: [Qemu-devel] [PATCH v2 6/6] tcg: cpu-exec: roll-up tb_find_fast/slow, (continued)
- Re: [Qemu-devel] [PATCH v2 6/6] tcg: cpu-exec: roll-up tb_find_fast/slow, Sergey Fedorov, 2016/07/07
- [Qemu-devel] [PATCH 2/3] tcg: Introduce tb_lock_locked(), Sergey Fedorov, 2016/07/07
- [Qemu-devel] [PATCH 1/3] tcg: Introduce mmap_lock_reset(), Sergey Fedorov, 2016/07/07
- [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/07
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Alex Bennée, 2016/07/07
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/07
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/07
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Alex Bennée, 2016/07/07
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/08
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/08
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(),
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/08
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/08
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/08
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/08
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/08
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/08
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/11
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Paolo Bonzini, 2016/07/11
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), Sergey Fedorov, 2016/07/11
Re: [Qemu-devel] [PATCH v2 0/6] Reduce lock contention on TCG hot-path, Emilio G. Cota, 2016/07/07