From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752452AbaHMIMc (ORCPT ); Wed, 13 Aug 2014 04:12:32 -0400 Received: from casper.infradead.org ([85.118.1.10]:43152 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752052AbaHMIM3 (ORCPT ); Wed, 13 Aug 2014 04:12:29 -0400 Date: Wed, 13 Aug 2014 10:12:15 +0200 From: Peter Zijlstra 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, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH v5 tip/core/rcu 15/16] rcu: Make RCU-tasks wait for idle tasks Message-ID: <20140813081215.GB9918@twins.programming.kicks-ass.net> References: <20140811224840.GA25594@linux.vnet.ibm.com> <1407797345-28227-1-git-send-email-paulmck@linux.vnet.ibm.com> <1407797345-28227-15-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="aObkNgyNMtBQZ80/" Content-Disposition: inline In-Reply-To: <1407797345-28227-15-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --aObkNgyNMtBQZ80/ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Aug 11, 2014 at 03:49:04PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" >=20 > Because idle-task code may need to be patched, RCU-tasks need to wait > for idle tasks to schedule. This commit therefore detects this case > via context switch. Block CPU hotplug during this time to avoid sending > IPIs to offline CPUs. >=20 > Note that checking for changes in the dyntick-idle counters is tempting, > but wrong. The reason that it is wrong is that a interrupt or NMI can > increment these counters without necessarily allowing the idle tasks to > make any forward progress. I'm going to NAK this.. with that rcu_idle patch I send there's typically only a single idle function thats out of bounds and if its more it can be made that with a bit of tlc to the cpuidle driver in question. This needs _FAR_ more justification than a maybe and a want. --aObkNgyNMtBQZ80/ Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJT6x3fAAoJEHZH4aRLwOS6YH4QAJXyxCbJY+mYDmTj/v6pFWKI 5syBZ0kG/fqCGw5ZAlwUYCcb2dlGmU9K2p52bwtX8RdTbKvA5qWdxhhs0oFoqWc4 DPo8fiP9MDeKMIDzPrx5YdmYORcSpC1LM/2CgBIaOLaJUn/49Cd4S+CHsqDJvT4o EqzgV7ROKijSmG+rKb1imdJynlH5fWCgyemyBIiGou0OLKh4zPB7TwiPBaYjmvbT dVWy5YXPJjSBHpWLJoKj/Gmv7dCoNoi5CBH0pawSHlNcvBhrdJgL5C3unXMW6r1o jppzZQkBhW0/9HWMa7DYlZfiIzCukHsEJznqr5BtUkVwDuAVQ7XookXYkEkjY4BC U8IBvGe39jYisGOHOcVgie4JqEhPB8W0H0dx6B6LNjX/yeRl0PyNBKb6CJvOKTz0 fz3Be2OjcdwnGWZFinRN3qKGxfZFNKsNC/zUM/JkGwoTlf0iuHhWIQinM47eX9B9 k8VdeXvg5TejXRBYcOClZ73MUWb0GtlkBD6oDCwIBjvcuGnIYM29lJyAGQcym35i mffrKRLJDDhm2XF8VRglsoCWOI5lbXlzvYjDbnoVrFdb+WF08ie+cCpW9B+sfGWZ Jcw+B7XiQbw9wAahd72OZXY9I2AplYHR0xP+hyiMUCPGBz3ssnLNSS4mPI6ijKik QqLR5H7hBZV5kEvrg+GC =zxKp -----END PGP SIGNATURE----- --aObkNgyNMtBQZ80/--