Message-ID: <49074A02.4080703@colorfullife.com>
Date: Tue, 28 Oct 2008 18:21:06 +0100
From: Manfred Spraul <manfred@colorfullife.com>
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       akpm@linux-foundation.org, dipankar@in.ibm.com,
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       rostedt@goodmis.org, peterz@infradead.org, penberg@cs.helsinki.fi,
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Subject: Re: [PATCH, RFC] v7 scalable classic RCU implementation
References: <20081015011143.GE6874@linux.vnet.ibm.com> <48F5A638.8020003@colorfullife.com> <20081015152637.GA6739@linux.vnet.ibm.com> <48FF73C7.90709@colorfullife.com> <20081022210254.GE6766@linux.vnet.ibm.com> <48FF9A0E.90205@colorfullife.com> <20081027164529.GC6783@linux.vnet.ibm.com> <49061AF0.8070106@colorfullife.com> <20081027235201.GK6783@linux.vnet.ibm.com> <4906A370.3000502@colorfullife.com> <20081028151738.GB6779@linux.vnet.ibm.com>
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Paul E. McKenney wrote:
>> How do you intend to handle nohz cpus?
>>     
>
> In which variant of RCU?  My current thought is to apply the rcutree.c
> version to rcupreempt.c.  If rcuclassic.c can be dropped, my thought
> would be to leave it alone -- it is unnecessarily awakening CPUs, but
> this is a non-fatal issue.
>
>   
For rcuclassic.

As far as  I can see, rcuclassic treats nohz cpus as always outside 
rcu_read_lock():
rcu_start_batch() contains
 >
 >                cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
 >
As soon as all cpus from rcp->cpumask reported a grace period, the 
callbacks are called.
That a bug, therefore I would drop rcuclassic as soon as rcutree is merged.

--
    Manfred

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