From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757150Ab2ERMO7 (ORCPT ); Fri, 18 May 2012 08:14:59 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:41839 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754645Ab2ERMO5 (ORCPT ); Fri, 18 May 2012 08:14:57 -0400 Date: Fri, 18 May 2012 05:14:01 -0700 From: "Paul E. McKenney" To: Pascal Chapperon Cc: Josh Boyer , linux-kernel@vger.kernel.org, kernel-team@fedoraproject.org Subject: Re: RCU related performance regression in 3.3 Message-ID: <20120518121401.GF2518@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120428034257.GA2495@linux.vnet.ibm.com> <20120501000245.GA4329@linux.vnet.ibm.com> <4F9FA50C.9070600@wanadoo.fr> <20120501154513.GD2441@linux.vnet.ibm.com> <4FA3EAEE.9030601@wanadoo.fr> <20120504150411.GC2411@linux.vnet.ibm.com> <4FA44CF9.7050604@wanadoo.fr> <20120504231442.GT2411@linux.vnet.ibm.com> <20120514223255.GA5719@linux.vnet.ibm.com> <4FB62C15.7080703@wanadoo.fr> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4FB62C15.7080703@wanadoo.fr> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12051812-1780-0000-0000-000005AF8E4A X-IBM-ISS-SpamDetectors: X-IBM-ISS-DetailInfo: BY=3.00000275; HX=3.00000188; KW=3.00000007; PH=3.00000001; SC=3.00000002; SDB=6.00140228; UDB=6.00032469; UTC=2012-05-18 12:14:55 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 18, 2012 at 01:01:41PM +0200, Pascal Chapperon wrote: > Le 15/05/2012 00:32, Paul E. McKenney a écrit : > >On Fri, May 04, 2012 at 04:14:42PM -0700, Paul E. McKenney wrote: > >>On Fri, May 04, 2012 at 11:41:13PM +0200, Pascal Chapperon wrote: > >>>Le 04/05/2012 17:04, Paul E. McKenney a écrit : > >>>>On Fri, May 04, 2012 at 04:42:54PM +0200, Pascal Chapperon wrote: > >>>>>Le 01/05/2012 17:45, Paul E. McKenney a écrit : > >>>>> > >>>>>>Here is my RCU_FAST_NO_HZ patch stack on top of v3.4-rc4. > >>>>>> > >>>>>>Or you can pull branch fnh.2012.05.01a from: > >>>>>> > >>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git > >>>>>> > >>>>>> Thanx, Paul > >>>>>> > >>>>>I applied your global patch on top of v3.4-rc4. But the slowdown is > >>>>>worse than before : boot sequence took 80s instead 20-30s (12s for > >>>>>initramfs instead of 2s). > >>>>> > >>>>>I'll send you rcu tracing log in a second mail. > >>>> > >>>>Hmmm... Well, I guess I am glad that I finally did something that > >>>>had an effect, but I sure wish that the effect had been in the other > >>>>direction! > >>>> > >>>>Just to make sure I understand: the difference between the 20-30s and > >>>>the 80s is exactly the patch I sent you? > >>>> > >>>> Thanx, Paul > >>>> > >>>> > >>>Yes. Exactly same kernel config as in previous results, I applied > >>>your patch against v3.4-rc4, and sorry, the result is exactly what I > >>>said; > >>>I saw that your global patch was quite huge, and addresses things which > >>>are not directly related with the initial patch (commit > >>>7cb92499000e3c86dae653077b1465458a039ef6); maybe a side effect? > >>> > >>>However, I'm ready to try this patch on my smaller laptop which > >>>supports well CONFIG_FAST_NO_HZ=y and systemd, if you think it can > >>>help ? > >>> > >>>Another thought: this issue as nothing to do with i7 Hyper-threading > >>>capacities ? (as I test core2duo, Pentium ulv in same conditions and I > >>>don't encountered any slowdown ?) > >> > >>Well, one possibility is that your setup starts the jiffies counter > >>at some interesting value. The attached patch (also against v3.4-rc4) > >>applies a bit more paranoia to the initialization to handle this > >>and other possibilities. > > > >This patchset fixes the problem where RCU_FAST_NO_HZ's timers were > >being ignored due to the dyntick-idle code having already calculated > >the CPU's wakeup time (which I sent earlier, mistakenly offlist), but > >also fixes a botched check in my workaround. > > > >Could you please try it out? This patch is against 3.4-rc4. > > > > Thanx, Paul > > > Hi Paul, > > < + if (!rcu_cpu_has_nonlazy_callbacks(cpu)) > --- > > + if (rcu_cpu_has_nonlazy_callbacks(cpu)) > > I was a little disappointed by the previous patch (boot sequence still > took 72 s.), but this one makes a huge difference ;-) > Slowdown during boot or shutdown with CONFIG_RCU_FAST_NO_HZ has > disappeared (~ 10 attempts) : > # systemd-analyze > Startup finished in 1990ms (kernel) + 1174ms (initramfs) + 3121ms > (userspace) = 6285ms > . Very good! And thank you very much for all your testing efforts and for bearing with me through this! Does this mean that I can add your Tested-by? > Do you want the rcu tracing log for this patch ? Could you please? Just in case there is some other surprise that I should know about that might not be visible. ;-) Thanx, Paul