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From: Wen Congyang <wency@cn.fujitsu.com>
Message-ID: <55B1B747.7000602@cn.fujitsu.com>
Date: Fri, 24 Jul 2015 11:55:51 +0800
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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: Paolo Bonzini <pbonzini@redhat.com>, Wen Congyang <ghostwcy@gmail.com>, Christian Borntraeger <borntraeger@de.ibm.com>, qemu-devel@nongnu.org

On 07/24/2015 12:58 AM, Paolo Bonzini wrote:
> 
> 
> 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. :/

Yes, it is a problem.

Thanks
Wen Congyang

> 
> 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.
>