From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754527AbcKYPxh (ORCPT ); Fri, 25 Nov 2016 10:53:37 -0500 Received: from mout.gmx.net ([212.227.15.18]:51038 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752149AbcKYPxg (ORCPT ); Fri, 25 Nov 2016 10:53:36 -0500 Message-ID: <1480089063.4075.80.camel@gmx.de> Subject: Re: RFC: documentation of the autogroup feature [v2] From: Mike Galbraith To: "Michael Kerrisk (man-pages)" Cc: Peter Zijlstra , Ingo Molnar , linux-man , lkml , Thomas Gleixner Date: Fri, 25 Nov 2016 16:51:03 +0100 In-Reply-To: References: <41d802dc-873a-ff02-17ff-93ce50f3e925@gmail.com> <1479901185.4306.38.camel@gmx.de> <327586fa-4672-d070-0ded-850654586273@gmail.com> <1479915229.4306.106.camel@gmx.de> <7513b0a5-c5d0-3a92-5849-995af22601e4@gmail.com> <1479921075.4306.153.camel@gmx.de> <1480078973.4075.58.camel@gmx.de> Content-Type: text/plain; charset="iso-2022-jp" X-Mailer: Evolution 3.16.5 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Provags-ID: V03:K0:dKAd4niGMGCg/RFIb5KXFylIfHPiD2nXdwz5sJgDSXol78zonCT DZHi7iI7w8EizNU3MygFyg3moEyCXQaVmOsTD6PmgBpLZhDpCn/80qRySXbqjkQhk6dFIsU 4PLzGtUU9i96PEhHwq9vQHhrR3Ryw6sXWPHPOki3Jb5mPjQVxs5PXabJnfdb4Sv4tiyzmlm Y79Y02JKKrbEA8TnM6Esg== X-UI-Out-Filterresults: notjunk:1;V01:K0:m9p1Jh61cm4=:6SkLJLjcRL5Y4sBW+jowtI +TWviHs4gcZ4BW6ydlXO2oUQCW6PdN72VK5ySI1gTVvWeRCLq33RP1qvCWr4V3r117Y0qu4zD oF1cYgziLr8XrDhNIdkUCA1zqWhF3S1xj7PYgZnjr8iX7W2DzQwZDtjCvDOIXPezSWMR7UYlB /3b8YGb3hNG+Zqz78l3tUAIXCW2A1gzW4sBu3/3/HKMPEdKGn1NuMZIOJe+4YR6OOFgRT0x1y Omtb9buhCNE4ujrevQLKvzlLoKgQaB/OtTwK2qgyAisZwo015H/tGUFW+yv3J9y0djyAIn6Jf u6ClHKiLhlaIpgM5ozbkzVlmN2mCphLCLonGff0dF/w7Ufd3DzJG5IyE78higmsTfAvF5ymyp RorVAlvoDSp5hjR6fqskWaFmvNyjq9UL5LsHQulqkM5DzOQith+ETxQGjRsTJP2ZBA8j5PseV Pzmd7q9gnSf603bVC09H2zcR+LUX/4ckwXnbcNgw2LA2TBxxxvU23ftSlpxgnXcdtZKil5Xvn ujUTvj5PSBZVGUGe8u3oPSSjbNtfiL2faGOzgAcVXuVuTQWbxS7IN7aJ3DXS3nvQNpsUW9Lkh iiaT57Ru/hGO7qTiE65gGRgR27WbiIwFuhx3Ci+8MsHoVNmEAY2ve2myWFnB4+jzYCxUMuJQv KijCzhpw8ltt4AtcIbW0/V5+MS88NPlbU8drhS0hqeilHm2dxKcDytqgQbceiHhBZDk0lQ7a2 T6XhvVFD41Yed+ErVFwnvrcYnXzURiYml3jCCiC1CqTNS8Tu7gEci92FW3m71xB8jzjFFLv3B aZoMnLW Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2016-11-25 at 16:04 +0100, Michael Kerrisk (man-pages) wrote: > > > ┌─────────────────────────────────────────────────────┐ > > > │FIXME │ > > > ├─────────────────────────────────────────────────────┤ > > > │How do the nice value of a process and the nice │ > > > │value of an autogroup interact? Which has priority? │ > > > │ │ > > > │It *appears* that the autogroup nice value is used │ > > > │for CPU distribution between task groups, and that │ > > > │the process nice value has no effect there. (I.e., │ > > > │suppose two autogroups each contain a CPU-bound │ > > > │process, with one process having nice==0 and the │ > > > │other having nice==19. It appears that they each │ > > > │get 50% of the CPU.) It appears that the process │ > > > │nice value has effect only with respect to schedul‐ │ > > > │ing relative to other processes in the *same* auto‐ │ > > > │group. Is this correct? │ > > > └─────────────────────────────────────────────────────┘ > > > > Yup, entity nice level affects distribution among peer entities. > > Huh! I only just learned about this via my experiments while > investigating autogroups. > > How long have things been like this? Always? (I don't think > so.) Since the arrival of CFS? Since the arrival of > autogrouping? (I'm guessing not.) Since some other point? > (When?) Always. Before CFS there just were no non-peers :) > It seems to me that this renders the traditional process > nice pretty much useless. (I bet I'm not the only one who'd > be surprised by the current behavior.) Yup, group scheduling is not a single edged sword, those don't exist. Box wide nice loss is not the only thing that can bite you, fairness, whether group or task oriented cuts both ways. -Mike