linux-kernel - Re: [RFC][PATCH 2/2] rcu classic: new algorithm for callbacks-processing(v2)

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Date:	Wed, 06 Aug 2008 15:08:10 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Ingo Molnar <mingo@...e.hu>, Dipankar Sarma <dipankar@...ibm.com>,
	Gautham Shenoy <ego@...ibm.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 2/2] rcu classic: new algorithm for	callbacks-processing(v2)

Paul E. McKenney wrote:
[...]
> 
> Tell me more about percpu_ptr().

Sorry about this. percpu_ptr is used for dynamic allocation percpu pointer.

It seems that we cannot get a pointer from a static declare percpu data
which can be used as a dynamic allocation percpu data's pointer. 

> 
[...]
> 
> I have a somewhat different goal here.  I want to simplify the memory
> ordering design without giving up too much performance -- the current
> state in mainline is much too fragile, in my opinion, especially given
> that the grace-period code paths are not fastpaths.
> 
> Next step -- hierarchical grace-period detection to handle the 4096-CPU
> machines that I was being buttonholed about at OLS...
> 
> Would you be interested in applying your multi-tailed list change to
> preemptable RCU?
> 
It's not necessary. Actually I like one tail per list which is good for
readability. 

But in my patch, the most work is combining lists, not
moving a list to next list, so i use multi-tailed simplify this works
and others(etc: "if (rdp->nxtlist)" will be changed to be a more
complex and less readability statement if i use one-tail-per-list)

These not means multi-tailed is good thing.

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