Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754107AbaFDII1 (ORCPT ); Wed, 4 Jun 2014 04:08:27 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:37201 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751387AbaFDIIX (ORCPT ); Wed, 4 Jun 2014 04:08:23 -0400 Date: Wed, 4 Jun 2014 10:08:09 +0200 From: Peter Zijlstra To: Vincent Guittot Cc: Morten Rasmussen , "mingo@kernel.org" , "linux-kernel@vger.kernel.org" , "linux@arm.linux.org.uk" , "linux-arm-kernel@lists.infradead.org" , "preeti@linux.vnet.ibm.com" , "efault@gmx.de" , "nicolas.pitre@linaro.org" , "linaro-kernel@lists.linaro.org" , "daniel.lezcano@linaro.org" Subject: Re: [PATCH v2 08/11] sched: get CPU's activity statistic Message-ID: <20140604080809.GK30445@twins.programming.kicks-ass.net> References: <1400860385-14555-1-git-send-email-vincent.guittot@linaro.org> <1400860385-14555-9-git-send-email-vincent.guittot@linaro.org> <20140528121001.GI19967@e103034-lin> <20140528154703.GJ19967@e103034-lin> <20140603155007.GZ30445@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="0Hxo4/sPH1pM8XTf" Content-Disposition: inline In-Reply-To: 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 --0Hxo4/sPH1pM8XTf Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Jun 04, 2014 at 09:47:26AM +0200, Vincent Guittot wrote: > On 3 June 2014 17:50, Peter Zijlstra wrote: > > On Wed, May 28, 2014 at 04:47:03PM +0100, Morten Rasmussen wrote: > >> Since we may do periodic load-balance every 10 ms or so, we will perfo= rm > >> a number of load-balances where runnable_avg_sum will mostly be > >> reflecting the state of the world before a change (new task queued or > >> moved a task to a different cpu). If you had have two tasks continuous= ly > >> on one cpu and your other cpu is idle, and you move one of the tasks to > >> the other cpu, runnable_avg_sum will remain unchanged, 47742, on the > >> first cpu while it starts from 0 on the other one. 10 ms later it will > >> have increased a bit, 32 ms later it will be 47742/2, and 345 ms later > >> it reaches 47742. In the mean time the cpu doesn't appear fully utiliz= ed > >> and we might decide to put more tasks on it because we don't know if > >> runnable_avg_sum represents a partially utilized cpu (for example a 50% > >> task) or if it will continue to rise and eventually get to 47742. > > > > Ah, no, since we track per task, and update the per-cpu ones when we > > migrate tasks, the per-cpu values should be instantly updated. > > > > If we were to increase per task storage, we might as well also track > > running_avg not only runnable_avg. >=20 > I agree that the removed running_avg should give more useful > information about the the load of a CPU. >=20 > The main issue with running_avg is that it's disturbed by other tasks > (as point out previously). As a typical example, if we have 2 tasks > with a load of 25% on 1 CPU, the unweighted runnable_load_avg will be > in the range of [100% - 50%] depending of the parallelism of the > runtime of the tasks whereas the reality is 50% and the use of > running_avg will return this value I'm not sure I see how 100% is possible, but yes I agree that runnable can indeed be inflated due to this queueing effect. --0Hxo4/sPH1pM8XTf Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJTjtPpAAoJEHZH4aRLwOS60zYP/1tdzup7DYmCbBBbJPnZ7rUN yGuEw8pVdmL16xAci+8Dle7PDOW9Lhn7KVkoVDTAp7UVcdKZWh4MEZi31vSZ5YXF R3uQv6dGmKqtIx7yeZWgtmJpPIEiD+dlV0ohmcwFet5D90vHZbIck8w2WJBLpe3K ihQfYH+pULITTG8CyOg010VrJptsupvZv3E4s35Lwv+HSr92tVbeJ8D57AI1/BLl fLbu+6wFEq+/GTqcPKuQqa9v40zFvFVRpvC9ttuXH/XbsxNIwl87An75u2qW8pPr /dQl3TxrIRJ/rAbLEAvqalux1GQ4xn+lHSBTgqUPBw7haPbmJuxzMtEz+E2luj+Q Tgqkl4Df/CoBuRXQD5dWKQCxbGvnx6j4OwwIsu+IltYZdX6r/ULJ3CW29zXTAUPk aHZgNHtqmxHnJkSk//BXYhIW6kvpwdmz1FoPavJuKNOSnGZlexADtW2Z3kX4+ZW6 Adym2NC/ympyDOtz296lBgwns4xKJdU83eF5JwpRY2yoZBDk8g6bOTR1sl9YcU3a p9rkE/TFHdc+ySq8tehoEyvexnk+Lqi02q35loXiwbfsalkD1XGMBA67xr2m2IoF MK7yOXP1vQ4hcBxlKqJAe0HFHQiY5UcnMFP9YJ1MxPKxOdGe0v3nkSK4vJEMvhCR 9tDbGkLlR4nO3+DW/IfV =gtRG -----END PGP SIGNATURE----- --0Hxo4/sPH1pM8XTf-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/