From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753188AbaHMNkk (ORCPT ); Wed, 13 Aug 2014 09:40:40 -0400 Received: from casper.infradead.org ([85.118.1.10]:44571 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753168AbaHMNkj (ORCPT ); Wed, 13 Aug 2014 09:40:39 -0400 Date: Wed, 13 Aug 2014 15:40:25 +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: <20140813134025.GN9918@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> <20140813081215.GB9918@twins.programming.kicks-ass.net> <20140813124818.GQ4752@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="t9kF86vOGmrWaBDV" Content-Disposition: inline In-Reply-To: <20140813124818.GQ4752@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 --t9kF86vOGmrWaBDV Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Aug 13, 2014 at 05:48:18AM -0700, Paul E. McKenney wrote: > On Wed, Aug 13, 2014 at 10:12:15AM +0200, Peter Zijlstra wrote: > > 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 send= ing > > > IPIs to offline CPUs. > > >=20 > > > Note that checking for changes in the dyntick-idle counters is tempti= ng, > > > 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. > >=20 > > 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. > >=20 > > This needs _FAR_ more justification than a maybe and a want. >=20 > Peter, your patch might be a good start, but I didn't see any reaction > from Steven or Masami and it did only x86. That's not an excuse for doing horrible things. And inventing new infra that needs to wake all CPUs is horrible. --t9kF86vOGmrWaBDV Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJT62rJAAoJEHZH4aRLwOS6R/gQAJWfG+j8jN5xgk8NPk7hdrZ/ jIvVzsxTX+GL2yYUza5rKRHl2AynPvgH92Au07ninkcHzSHFptHL7MxfKfqdztYW rcQnHXw0DRigY+LB86TkgEs7paLIt/Qjp6OtEjwyVqyVElCzgLhWx0aFGASR5usV DVv0ASYrRg9gaPzCSLsUilgyB9JeQEi/571YkDJRpkpedn3IXToWgz50AyQ5/eKJ jgKQ2t5dQzzFt3B/JQHP+je+4qJJ0uZdNKSf6ddHSvLc2nM3FzDs1yGgn28H6nSZ qLeekfKlmVj/gIGJLTe5GLCk/731FK43aQGYB+RXw+AmEy++jKP5PwShmCgTVEVo HDvMm90GsbuSBw6zTbbiuN8lyFllV5jjsokksa62fbo977p3+LeiB8i7eYkGMT8f hBEbNBGdZwkybW8MX/ZZtyZAzCQMHqMnnbO7+BesccTpD+vEnLwxc1PtvQTqheXs M7lDDNdwJkOKGxRTRyvBIJyeMaHnRXESRpsPgyGfoBgLG7uU6TwB6gDBj28+ttgt FD3N9OmxnUk410nCvHT83msda+P51lzdMQU8BwJGf9GjVWJju8iiTcPYQMl1TW/W guZ7wybD7o4ceIwJ32ZzBCiYIWJq+SdVzcAVQpntihTk/XytqpwQroLiHReg8SzW ADdrgu88eRpqdE2v1Czg =Ljva -----END PGP SIGNATURE----- --t9kF86vOGmrWaBDV--