From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0385DC3A5A1 for ; Wed, 28 Aug 2019 14:48:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D645922CED for ; Wed, 28 Aug 2019 14:48:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726702AbfH1OsA (ORCPT ); Wed, 28 Aug 2019 10:48:00 -0400 Received: from shelob.surriel.com ([96.67.55.147]:32774 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726272AbfH1OsA (ORCPT ); Wed, 28 Aug 2019 10:48:00 -0400 Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92) (envelope-from ) id 1i2zEi-00018S-V1; Wed, 28 Aug 2019 10:47:48 -0400 Message-ID: <98dffa226df25fd0d3017605bc7343c330f79a7e.camel@surriel.com> Subject: Re: [PATCH 03/15] sched,fair: redefine runnable_load_avg as the sum of task_h_load From: Rik van Riel To: Vincent Guittot Cc: linux-kernel , Kernel Team , Paul Turner , Dietmar Eggemann , Peter Zijlstra , Ingo Molnar , Morten Rasmussen , Thomas Gleixner , Mel Gorman Date: Wed, 28 Aug 2019 10:47:48 -0400 In-Reply-To: References: <20190822021740.15554-1-riel@surriel.com> <20190822021740.15554-4-riel@surriel.com> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-/JNyIUHGgxPk9J2Mpf6W" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-/JNyIUHGgxPk9J2Mpf6W Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2019-08-28 at 15:50 +0200, Vincent Guittot wrote: > Hi Rik, >=20 > On Thu, 22 Aug 2019 at 04:18, Rik van Riel wrote: > > The runnable_load magic is used to quickly propagate information > > about > > runnable tasks up the hierarchy of runqueues. The runnable_load_avg > > is > > mostly used for the load balancing code, which only examines the > > value at > > the root cfs_rq. > >=20 > > Redefine the root cfs_rq runnable_load_avg to be the sum of > > task_h_loads > > of the runnable tasks. This works because the hierarchical > > runnable_load of > > a task is already equal to the task_se_h_load today. This provides > > enough > > information to the load balancer. > >=20 > > The runnable_load_avg of the cgroup cfs_rqs does not appear to be > > used for anything, so don't bother calculating those. > >=20 > > This removes one of the things that the code currently traverses > > the > > cgroup hierarchy for, and getting rid of it brings us one step > > closer > > to a flat runqueue for the CPU controller. >=20 > I like your proposal but just wanted to clarify one thing with this > patch. > Although you removed the computation of runnable_load_avg of the > cgroup cfs_rq, we are still traversing the hierarchy to update the > root cfs_rq runnable_load_avg because we are traversing the hierarchy > for computing the task_h_loads The task_h_load hierarchy traversal in update_cfs_rq_h_load is rate limited to once a jiffy, though. Rate limiting the hierarchy traversal significantly reduces overhead. > That being said, if we manage to remove the need on using > runnable_load_avg we will completely skip this traversal. I have a > proposal to remove it from load balance and wake up path but i > haven't > look at numa stats which also use it --=20 All Rights Reversed. --=-/JNyIUHGgxPk9J2Mpf6W Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEEKR73pCCtJ5Xj3yADznnekoTE3oMFAl1mlBQACgkQznnekoTE 3oOFkQf/bkexA5aKlLDWB+jCZChFVrZFJHgookxSOQ7SrsAze5zYeir8BRCJDEyE 60uxGiByPBTetwFYRexQKM7Q83Ny3QXB03gv3LYqzYI2sLYwDR+zl6C8eDZvOcLc GYfbaNHj5gV0JoZ8i4BCg4pNzRTxOtVLLdcWBTCRi+TFiVLd2O5IZL0A1spmFoyc mu+b7HwyRbbTp2qp9PJZNL7x1uyj/kDl9+Ofnti6VDEfHCrBA6PwvQ0DtFYT5/lA 5jjs3lXis3opt50pMytwN2FTN6G2FXV/kaWBkYwDDMe4uVXB4J1XG322o/NGlxJA IadW9EJLhydE3ey+pofu8w4qM73gNA== =g1cO -----END PGP SIGNATURE----- --=-/JNyIUHGgxPk9J2Mpf6W--