From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757079AbaFTVYb (ORCPT ); Fri, 20 Jun 2014 17:24:31 -0400 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:46881 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756102AbaFTVYa (ORCPT ); Fri, 20 Jun 2014 17:24:30 -0400 Date: Fri, 20 Jun 2014 14:24:23 -0700 From: josh@joshtriplett.org To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, 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 tip/core/rcu 0/5] Fix for cond_resched performance regression Message-ID: <20140620212423.GA22886@cloud> References: <20140620183249.GA6325@linux.vnet.ibm.com> <20140620191236.GA10340@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140620191236.GA10340@linux.vnet.ibm.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 20, 2014 at 12:12:36PM -0700, Paul E. McKenney wrote: > o Make cond_resched() a no-op for PREEMPT=y. This might well turn > out to be a good thing, but it doesn't help give RCU the quiescent > states that it needs. What about doing this, together with letting the fqs logic poke un-quiesced kernel code as needed? That way, rather than having cond_resched do any work, you have the fqs logic recognize that a particular CPU has gone too long without quiescing, without disturbing that CPU at all if it hasn't gone too long. - Josh Triplett