From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760175AbaGDVU4 (ORCPT ); Fri, 4 Jul 2014 17:20:56 -0400 Received: from e38.co.us.ibm.com ([32.97.110.159]:44508 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759909AbaGDVUy (ORCPT ); Fri, 4 Jul 2014 17:20:54 -0400 Date: Fri, 4 Jul 2014 14:20:45 -0700 From: "Paul E. McKenney" To: Mike Galbraith Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, riel@redhat.com, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu Subject: Re: [PATCH RFC tip/core/rcu] Parallelize and economize NOCB kthread wakeups Message-ID: <20140704212045.GM4603@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20140702153915.GQ4603@linux.vnet.ibm.com> <20140702160412.GO19379@twins.programming.kicks-ass.net> <20140702170838.GS4603@linux.vnet.ibm.com> <1404358279.5137.63.camel@marge.simpson.net> <20140703052124.GB4603@linux.vnet.ibm.com> <1404366520.5137.90.camel@marge.simpson.net> <20140703162944.GG4603@linux.vnet.ibm.com> <1404444236.5756.36.camel@marge.simpson.net> <20140704050541.GL4603@linux.vnet.ibm.com> <1404453694.5756.111.camel@marge.simpson.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1404453694.5756.111.camel@marge.simpson.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14070421-1344-0000-0000-0000029DBCA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 04, 2014 at 08:01:34AM +0200, Mike Galbraith wrote: > On Thu, 2014-07-03 at 22:05 -0700, Paul E. McKenney wrote: > > On Fri, Jul 04, 2014 at 05:23:56AM +0200, Mike Galbraith wrote: > > > > Turn it on and don't worry about it is exactly what distros want the > > > obscure feature with very few users to be. Last time I did a drive-by, > > > my boxen said I should continue to worry about it ;-) > > > > Yep, which is the reason for the patch on the last email. > > > > Then again, exactly which feature and which reason for worry? > > NO_HZ_FULL. I tried ALL a while back, box instantly called me an idiot. > Maybe that has improved since, dunno. Ah, I was thinking in terms of RCU_CPU_NOCB. > Last drive-by I didn't do much overhead measurement, stuck mostly > functionality, and it still had rough edges that enterprise users may > not fully appreciate. Trying to let 60 of 64 cores do 100% compute > showed some cores having a hard time entering tickless at all, and > ~200us spikes that I think are due to tick losing skew.. told Frederic > I'd take a peek at that, but haven't had time yet. There were other > known things as well, like timers and workqueues for which there are > patches floating around. All in all, it was waving the men at work > sign, pointing at the "Say N" by the config option, and suggesting that > ignoring that would not be the cleverest of moves. Well, I am not going to join a debate on Kconfig default selection. ;-) I will say that two years ago, setting NO_HZ_FULL=y by default would have been insane. Perhaps soon it will be a no-brainer, and I am of course trying to bring that day closer. Right now it is of course a judgment call. Thanx, Paul