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
