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Re: [Qemu-devel] [PATCH] rcu: actually register threads that have RCU re

From: Wen Congyang
Subject: Re: [Qemu-devel] [PATCH] rcu: actually register threads that have RCU read-side critical sections
Date: Fri, 24 Jul 2015 11:55:51 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0

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.

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.

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