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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: |
Mon, 11 Jul 2016 16:03:42 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 |
On 11/07/2016 15:06, Sergey Fedorov wrote:
> On 08/07/16 23:52, Paolo Bonzini wrote:
>>
>> On 08/07/2016 22:24, Sergey Fedorov wrote:
>>> I remember, I've just found that we discussed it in this thread:
>>>
>>> http://thread.gmane.org/gmane.comp.emulators.qemu/401723/focus=406852
>>>
>>> I was thinking of just doing 'tb_jmp_cache' lookup out of the lock, not
>>> tb_find_physical(). Now thanks to QHT, we could do tb_find_physical()
>>> out of the lock, too. This changes things.
>> But in my patch ("tcg: move tb_find_fast outside the tb_lock critical
>> section", which originally was written by Fred---most of my contribution
>> was getting the invalidation right, not the lock-free lookup)
>> tb_find_physical was also done out of the lock. It was then retried
>> inside the lock, if it failed.
>>
>> This is why I needed to fail all concurrent lookups as the first step in
>> the invalidation.
>>
>> Emilio's QHT resulted in a rewrite of tb_find_physical, but the basic
>> concepts are the same.
>
> That could work, I think, if we re-check under tb_lock whether the TB is
> still valid before adding a direct jump to it.
Right, this can still happen:
tb_find_fast tb_phys_invalidate
tb_lock
jmp_cache miss
-> tb_find_slow
-> tb_find_physical
QHT hit
tb_lock
invalidate tb->pc
remove from lists
tb_unlock
tb_add_jump
tb_unlock
I seem to recall that Emilio added a seqlock for this purpose, but
adding a tb_check_invalidated(TranslationBlock *tb) inline function will
also do.
Paolo
- Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump(), (continued)
- 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, 2016/07/08
- 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 <=
- 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