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Message-ID: <20120316154623.GA28403@sgi.com> Date: Fri, 16 Mar 2012 10:46:23 -0500 From: Dimitri Sivanich <sivanich@....com> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org Subject: Re: [PATCH RFC] rcu: Limit GP initialization to CPUs that have been online On Thu, Mar 15, 2012 at 02:07:53PM -0700, Paul E. McKenney wrote: > On Thu, Mar 15, 2012 at 11:23:14AM -0700, Paul E. McKenney wrote: > > On Thu, Mar 15, 2012 at 12:58:57PM -0500, Dimitri Sivanich wrote: > > > On Wed, Mar 14, 2012 at 09:56:57AM -0700, Paul E. McKenney wrote: > > > > On Wed, Mar 14, 2012 at 08:17:17AM -0700, Paul E. McKenney wrote: > > > > > On Wed, Mar 14, 2012 at 08:08:01AM -0500, Dimitri Sivanich wrote: > > > > > > On Wed, Mar 14, 2012 at 01:40:41PM +0100, Mike Galbraith wrote: > > > > > > > On Wed, 2012-03-14 at 10:24 +0100, Mike Galbraith wrote: > > > > > > > > On Tue, 2012-03-13 at 17:24 -0700, Paul E. McKenney wrote: > > > > > > > > > The following builds, but is only very lightly tested. Probably full > > > > > > > > > of bug, especially when exercising CPU hotplug. > > > > > > > > > > > > > > > > You didn't say RFT, but... > > > > > > > > > > > > > > > > To beat on this in a rotund 3.0 kernel, the equivalent patch would be > > > > > > > > the below? My box may well answer that before you can.. hope not ;-) > > > > > > > > > > > > > > (Darn, it did. Box says boot stall with virgin patch in tip too though. > > > > > > > Wedging it straight into 3.0 was perhaps a tad premature;) > > > > > > > > > > > > I saw the same thing with 3.3.0-rc7+ and virgin patch on UV. Boots fine without the patch. > > > > > > > > > > Right... Bozo here forgot to set the kernel parameters for large-system > > > > > emulation during testing. Apologies for the busted patch, will fix. > > > > > > > > > > And thank you both for the testing!!! > > > > > > > > > > Hey, at least I labeled it "RFC". ;-) > > > > > > > > Does the following work better? It does pass my fake-big-system tests > > > > (more testing in the works). > > > > > > This one stalls for me at the same place the other one did. Once again, > > > if I remove the patch and rebuild, it boots just fine. > > > > > > Is there some debug/trace information that you would like me to provide? > > > > Very strange. > > > > Could you please send your dmesg and .config? > > Hmmm... Memory ordering could be a problem, though in that case I would > have expected the hand during the onlining process. However, the memory > ordering does need to be cleaned up in any case, please see below. > After testing this on 3.3.0-rc7+ I can say that this very much improves the latency in the two rcu_for_each_node_breadth_first() loops. Without the patch, under moderate load and while running an interrupt latency test, I see the majority of loops taking 100-200 usec. With the patch there are a few that take between 20-30, the rest are below that. Not that everything is OK latency-wise in RCU land. There is still an interrupt holdoff in force_quiescent_state() that is taking > 100usec, with or without the patch. I'm having difficulty finding exactly where the other holdoff is happening because the kernel isn't accepting my nmi handler. That said, this fix is a nice improvement in those two loops. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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