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

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Message-ID: <49061AF0.8070106@colorfullife.com>
Date:	Mon, 27 Oct 2008 20:48:00 +0100
From:	Manfred Spraul <manfred@...orfullife.com>
To:	paulmck@...ux.vnet.ibm.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

Paul E. McKenney wrote:
> 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.
>   
Two implementations. IMHO the current rcu-classic code should be dropped 
immediately when you add rcu-tree:
rcu-classic is buggy, as far as I can see long-running interrupts on 
nohz cpus are not handled correctly. I don't think it makes sense to 
keep it in the kernel in parallel to rcu-tree.

I would propose that rcu-tree replaces rcu-classic.
I'll continue to update rcu-state, I think that it will achieve lower 
latency than rcu-tree [average/max time between call_rcu() and 
destruction callback] and it doesn't have the irq disabled loop to find 
the missing cpus.
If I find decent benchmarks where I can quantify the advantages, then 
I'll propose to merge rcu-state as a third implementation in addition to 
rcu-tree and rcu-preempt.

Paul: What do you think?

--
    Manfred


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