linux-kernel - Re: [PATCH, RFC] v7 scalable classic RCU implementation

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Message-ID: <20081027164529.GC6783@linux.vnet.ibm.com>
Date:	Mon, 27 Oct 2008 09:45:29 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	mingo@...e.hu, akpm@...ux-foundation.org, dipankar@...ibm.com,
	josht@...ux.vnet.ibm.com, schamp@....com, niv@...ibm.com,
	dvhltc@...ibm.com, ego@...ibm.com, laijs@...fujitsu.com,
	rostedt@...dmis.org, peterz@...radead.org, penberg@...helsinki.fi,
	andi@...stfloor.org, tglx@...utronix.de
Subject: Re: [PATCH, RFC] v7 scalable classic RCU implementation

On Wed, Oct 22, 2008 at 11:24:30PM +0200, Manfred Spraul wrote:
> Paul E. McKenney wrote:
>> Hmmm...  Looks like rcu_pending is also always called with its cpu
>> parameter set to the current CPU, and same for rcu_needs_cpu().
>> And given that all the external uses of rcu_check_callbacks() are
>> of the following form:
>>
>> 	if (rcu_pending(cpu))
>> 		rcu_check_callbacks(cpu, whatever);
>>
>>
>> perhaps rcu_pending() should be an internal-to-RCU API invoked from
>> rcu_check_callbacks().
>>
>> Thoughts?
>>   
> From my point of view: Yes, change it.
>
> In the long run, I'd like to move the stall detector code to rcupdate.c, 
> with an 'rcu_cpu_missing' callback. That one would need a cpu flag, but 
> that's a new function.

Agreed.  Perhaps a good change to make while introducing stall detection
to preemptable RCU -- there would then be three examples, which should
allow good generalization.

							Thanx, Paul
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