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Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path
From: |
Emilio G. Cota |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path |
Date: |
Fri, 1 Jul 2016 20:39:42 -0400 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Fri, Jul 01, 2016 at 17:16:10 +0100, Alex Bennée wrote:
> Lock contention in the hot path of moving between existing patched
> TranslationBlocks is the main drag in multithreaded performance. This
> patch pushes the tb_lock() usage down to the two places that really need
> it:
>
> - code generation (tb_gen_code)
> - jump patching (tb_add_jump)
>
> The rest of the code doesn't really need to hold a lock as it is either
> using per-CPU structures, atomically updated or designed to be used in
> concurrent read situations (qht_lookup).
>
> To keep things simple I removed the #ifdef CONFIG_USER_ONLY stuff as the
> locks become NOPs anyway until the MTTCG work is completed.
>From a scalability point of view it would be better to have a single
critical section.
>From a correctness point of view, we're reading tb->page_addr[1]
without holding a lock. This field is set after qht_insert(tb),
so we might read a yet-uninitialized value.
I propose to just extend the critical section, like we used to
do with tcg_lock_reset.
Emilio
- [Qemu-devel] [PATCH 0/2] Reduce lock contention on TCG hot-path, Alex Bennée, 2016/07/01
- [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Alex Bennée, 2016/07/01
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Richard Henderson, 2016/07/01
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path,
Emilio G. Cota <=
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Alex Bennée, 2016/07/04
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Emilio G. Cota, 2016/07/04
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Alex Bennée, 2016/07/05
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Paolo Bonzini, 2016/07/05
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Alex Bennée, 2016/07/05
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Paolo Bonzini, 2016/07/05
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Sergey Fedorov, 2016/07/05
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Alex Bennée, 2016/07/05
- Re: [Qemu-devel] [PATCH 2/2] cpu-exec: remove tb_lock from the hot-path, Sergey Fedorov, 2016/07/05
[Qemu-devel] [PATCH 1/2] tcg: Ensure safe tb_jmp_cache lookup out of 'tb_lock', Alex Bennée, 2016/07/01