linux-kernel - Re: [PATCH, RFC] v6 scalable classic RCU implementation

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Message-ID: <20080925141809.GB6725@linux.vnet.ibm.com>
Date:	Thu, 25 Sep 2008 07:18:09 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	akpm@...ux-foundation.org, manfred@...orfullife.com,
	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.com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH, RFC] v6 scalable classic RCU implementation

On Thu, Sep 25, 2008 at 09:29:15AM +0200, Ingo Molnar wrote:
> 
> * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > Attached is an updated patch to Classic RCU that applies a hierarchy, 
> > greatly reducing the contention on the top-level lock for large 
> > machines.  This passes 10-hour concurrent rcutorture and 
> > online-offline testing on 128-CPU ppc64 without dynticks enabled, and 
> > exposes some timekeeping bugs in presence of dynticks (exciting 
> > working on a system where "sleep 1" hangs until interrupted...).
> 
> i'm wondering about those timekeeping bugs. Do you have an idea what's 
> it about and does it affect mainline?

Sad to say, they do affect mainline -- I can reproduce these problems
in 2.6.27-rc7.  Thomas has given me a couple of fixes that got rid of
earlier problems in which jiffies would stop counting, and I believe
has located the cause of at least one other problem.

							Thanx, Paul
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