From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: regression caused by 08f511fd41c3 ("cpufreq: Reduce cpufreq_update_util() overhead a bit") Date: Fri, 17 Jun 2016 06:16:51 -0700 Message-ID: <20160617131651.GU3923@linux.vnet.ibm.com> References: <20160617163023.5bb374f8@xhacker> <20160617164054.6339c5d4@xhacker> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: "Rafael J. Wysocki" Cc: Jisheng Zhang , Peter Zijlstra , "Rafael J. Wysocki" , Viresh Kumar , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List List-Id: linux-pm@vger.kernel.org On Fri, Jun 17, 2016 at 03:09:36PM +0200, Rafael J. Wysocki wrote: > On Fri, Jun 17, 2016 at 10:40 AM, Jisheng Zhang wrote: > > Dear all, > > > > On Fri, 17 Jun 2016 16:30:23 +0800 Jisheng Zhang wrote: > > > >> Dear all, > >> > >> I found one regression: In an idle system, wakeups/s (reported by powertop) > >> is increased a lot, e.g on a intel snb 4 core platform, the wakeup event > >> number is increased from 8 wakeups/s to 24 wakeup/s. bisect points to > >> this commit. I could send detailed bisect log if it's wanted. > >> > > > > more information maybe useful: after the commit, the top two wakeup source > > are > > > > Process [rcu_sched] > > > > Timer tick_sched_timer > > And what was there before the commit? > > Granted, I'm not seeing this on my systems. > > Paul, Peter, any ideas about what may be going on here? Looks to me like this commit moved some code from synchronize_rcu() to synchronize_sched(). Assuming that this is a CONFIG_PREEMPT=y system, might there have been a decrease in the wakeups from the rcu_preempt kthread? Thanx, Paul