From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750754AbWB0Lkd (ORCPT ); Mon, 27 Feb 2006 06:40:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751027AbWB0Lkd (ORCPT ); Mon, 27 Feb 2006 06:40:33 -0500 Received: from seldon.control.lth.se ([130.235.83.40]:49884 "EHLO seldon.control.lth.se") by vger.kernel.org with ESMTP id S1750754AbWB0Lkd (ORCPT ); Mon, 27 Feb 2006 06:40:33 -0500 Message-ID: <4402E52F.6080409@control.lth.se> Date: Mon, 27 Feb 2006 12:40:31 +0100 From: Martin Andersson User-Agent: Mozilla Thunderbird 1.0.7 (X11/20050923) X-Accept-Language: en-us, en MIME-Version: 1.0 To: linux-kernel@vger.kernel.org Subject: Strange interactivity behaviour Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Possible Problem: There may be a truncation error in kernel/sched.c triggered when the nice value is negative. The affected code is used in the TASK_INTERACTIVE macro. The code is: #define SCALE(v1,v1_max,v2_max) \ (v1) * (v2_max) / (v1_max) which is used in this way: SCALE(TASK_NICE(p), 40, MAX_BONUS) Comments in the code says: * This part scales the interactivity limit depending on niceness. * * We scale it linearly, offset by the INTERACTIVE_DELTA delta. * Here are a few examples of different nice levels: * * TASK_INTERACTIVE(-20): [1,1,1,1,1,1,1,1,1,0,0] * TASK_INTERACTIVE(-10): [1,1,1,1,1,1,1,0,0,0,0] * TASK_INTERACTIVE( 0): [1,1,1,1,0,0,0,0,0,0,0] * TASK_INTERACTIVE( 10): [1,1,0,0,0,0,0,0,0,0,0] * TASK_INTERACTIVE( 19): [0,0,0,0,0,0,0,0,0,0,0] * * (the X axis represents the possible -5 ... 0 ... +5 dynamic * priority range a task can explore, a value of '1' means the * task is rated interactive.) However, the current code does not scale it linearly and the result differs from the given examples. If the mathematical function "floor" is used when the nice value is negative instead of the truncation one gets when using integer division, the result conforms to the documentation. I belive that this is a bug. Is this correct or have i misunderstood something? /Martin Andersson --- Output of TASK_INTERACTIVE when using the kernel code: nice dynamic priorities -20 1 1 1 1 1 1 1 1 1 0 0 -19 1 1 1 1 1 1 1 1 0 0 0 -18 1 1 1 1 1 1 1 1 0 0 0 -17 1 1 1 1 1 1 1 1 0 0 0 -16 1 1 1 1 1 1 1 1 0 0 0 -15 1 1 1 1 1 1 1 0 0 0 0 -14 1 1 1 1 1 1 1 0 0 0 0 -13 1 1 1 1 1 1 1 0 0 0 0 -12 1 1 1 1 1 1 1 0 0 0 0 -11 1 1 1 1 1 1 0 0 0 0 0 -10 1 1 1 1 1 1 0 0 0 0 0 -9 1 1 1 1 1 1 0 0 0 0 0 -8 1 1 1 1 1 1 0 0 0 0 0 -7 1 1 1 1 1 0 0 0 0 0 0 -6 1 1 1 1 1 0 0 0 0 0 0 -5 1 1 1 1 1 0 0 0 0 0 0 -4 1 1 1 1 1 0 0 0 0 0 0 -3 1 1 1 1 0 0 0 0 0 0 0 -2 1 1 1 1 0 0 0 0 0 0 0 -1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 1 0 0 0 0 0 0 0 2 1 1 1 1 0 0 0 0 0 0 0 3 1 1 1 1 0 0 0 0 0 0 0 4 1 1 1 0 0 0 0 0 0 0 0 5 1 1 1 0 0 0 0 0 0 0 0 6 1 1 1 0 0 0 0 0 0 0 0 7 1 1 1 0 0 0 0 0 0 0 0 8 1 1 0 0 0 0 0 0 0 0 0 9 1 1 0 0 0 0 0 0 0 0 0 10 1 1 0 0 0 0 0 0 0 0 0 11 1 1 0 0 0 0 0 0 0 0 0 12 1 0 0 0 0 0 0 0 0 0 0 13 1 0 0 0 0 0 0 0 0 0 0 14 1 0 0 0 0 0 0 0 0 0 0 15 1 0 0 0 0 0 0 0 0 0 0 16 0 0 0 0 0 0 0 0 0 0 0 17 0 0 0 0 0 0 0 0 0 0 0 18 0 0 0 0 0 0 0 0 0 0 0 19 0 0 0 0 0 0 0 0 0 0 0 Output of TASK_INTERACTIVE when using "floor" nice dynamic priorities -20 1 1 1 1 1 1 1 1 1 0 0 -19 1 1 1 1 1 1 1 1 1 0 0 -18 1 1 1 1 1 1 1 1 1 0 0 -17 1 1 1 1 1 1 1 1 1 0 0 -16 1 1 1 1 1 1 1 1 0 0 0 -15 1 1 1 1 1 1 1 1 0 0 0 -14 1 1 1 1 1 1 1 1 0 0 0 -13 1 1 1 1 1 1 1 1 0 0 0 -12 1 1 1 1 1 1 1 0 0 0 0 -11 1 1 1 1 1 1 1 0 0 0 0 -10 1 1 1 1 1 1 1 0 0 0 0 -9 1 1 1 1 1 1 1 0 0 0 0 -8 1 1 1 1 1 1 0 0 0 0 0 -7 1 1 1 1 1 1 0 0 0 0 0 -6 1 1 1 1 1 1 0 0 0 0 0 -5 1 1 1 1 1 1 0 0 0 0 0 -4 1 1 1 1 1 0 0 0 0 0 0 -3 1 1 1 1 1 0 0 0 0 0 0 -2 1 1 1 1 1 0 0 0 0 0 0 -1 1 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 1 0 0 0 0 0 0 0 2 1 1 1 1 0 0 0 0 0 0 0 3 1 1 1 1 0 0 0 0 0 0 0 4 1 1 1 0 0 0 0 0 0 0 0 5 1 1 1 0 0 0 0 0 0 0 0 6 1 1 1 0 0 0 0 0 0 0 0 7 1 1 1 0 0 0 0 0 0 0 0 8 1 1 0 0 0 0 0 0 0 0 0 9 1 1 0 0 0 0 0 0 0 0 0 10 1 1 0 0 0 0 0 0 0 0 0 11 1 1 0 0 0 0 0 0 0 0 0 12 1 0 0 0 0 0 0 0 0 0 0 13 1 0 0 0 0 0 0 0 0 0 0 14 1 0 0 0 0 0 0 0 0 0 0 15 1 0 0 0 0 0 0 0 0 0 0 16 0 0 0 0 0 0 0 0 0 0 0 17 0 0 0 0 0 0 0 0 0 0 0 18 0 0 0 0 0 0 0 0 0 0 0 19 0 0 0 0 0 0 0 0 0 0 0