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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Thu, 23 Jul 2015 18:58:14 +0200
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Subject: Re: [Qemu-devel] [PATCH] rcu: actually register threads that have
 RCU read-side critical sections
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To: Wen Congyang <ghostwcy@gmail.com>, Wen Congyang <wency@cn.fujitsu.com>, Christian Borntraeger <borntraeger@de.ibm.com>, qemu-devel@nongnu.org



On 23/07/2015 14:59, Wen Congyang wrote:
>>>
>>> If the thread doesn't use RCU, rcu_register_thread() is harmless, is
>>> it right?
>>
>> Every rcu_register_thread() makes synchronize_rcu() a little slower.
> 
> Yes, but synchronize_rcu() is very slow...

Hmm, worse, rcu_register_thread() if called together with
synchronize_rcu() it waits for the synchronize_rcu() to finish. :/

Paolo

>>
>>>>> be simpler to add an assertion in rcu_register_thread.  I'm just a bit
>>>>> wary of doing little more than the bare minimum in 2.4, because of the
>>>>> OS X failure that I didn't quite understand.
>>> Which problem? I don't find it in the maillist.
>>
>> http://article.gmane.org/gmane.comp.emulators.qemu/351548
> 
> Hmm, I guess rcu_reader is invalid when pthread key is destroyed.
> pthread key and __thread
> variable, which is destroyed first? I don't find any document to
> describe it.