From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761295Ab1EARvT (ORCPT ); Sun, 1 May 2011 13:51:19 -0400 Received: from mailout-de.gmx.net ([213.165.64.22]:46916 "HELO mailout-de.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1761271Ab1EARvS (ORCPT ); Sun, 1 May 2011 13:51:18 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1+TyhEnzoSTThkNJzAy7AcbUH0TLbqB0fjui9F981 yqlkP5cydUKoqQ Subject: Re: [PATCH tip/core/rcu 31/86] rcu: further lower priority in rcu_yield() From: Mike Galbraith To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org, "Paul E. McKenney" In-Reply-To: <1304256126-26015-31-git-send-email-paulmck@linux.vnet.ibm.com> References: <20110501132142.GA25494@linux.vnet.ibm.com> <1304256126-26015-31-git-send-email-paulmck@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Sun, 01 May 2011 19:51:04 +0200 Message-ID: <1304272264.7417.20.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.32.1 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2011-05-01 at 06:21 -0700, Paul E. McKenney wrote: > From: Paul E. McKenney > > Although rcu_yield() dropped from real-time to normal priority, there > is always the possibility that the competing tasks have been niced. > So nice to 19 in rcu_yield() to help ensure that other tasks have a > better chance of running. But.. that just prolongs the pain of overhead you _have_ to eat, no? In a brief surge, fine, you can spread the cost out.. but how do you know when it's ok to yield? (When maintenance threads worrying about their CPU usage is worrisome.) > Signed-off-by: Paul E. McKenney > Signed-off-by: Paul E. McKenney > --- > kernel/rcutree.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index 3295c7b..963b4b1 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -1561,6 +1561,7 @@ static void rcu_yield(void (*f)(unsigned long), unsigned long arg) > mod_timer(&yield_timer, jiffies + 2); > sp.sched_priority = 0; > sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp); > + set_user_nice(current, 19); > schedule(); > sp.sched_priority = RCU_KTHREAD_PRIO; > sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);