From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933667Ab2ERLBu (ORCPT ); Fri, 18 May 2012 07:01:50 -0400 Received: from smtp12.smtpout.orange.fr ([80.12.242.134]:55632 "EHLO smtp.smtpout.orange.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933168Ab2ERLBs convert rfc822-to-8bit (ORCPT ); Fri, 18 May 2012 07:01:48 -0400 Message-ID: <4FB62C15.7080703@wanadoo.fr> Date: Fri, 18 May 2012 13:01:41 +0200 From: Pascal Chapperon User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: Josh Boyer , linux-kernel@vger.kernel.org, kernel-team@fedoraproject.org Subject: Re: RCU related performance regression in 3.3 References: <20177034.34764.1335528920975.JavaMail.www@wwinf1f04> <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> In-Reply-To: <20120514223255.GA5719@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 . Do you want the rcu tracing log for this patch ? Pascal