Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754498Ab1D1HHl (ORCPT ); Thu, 28 Apr 2011 03:07:41 -0400 Received: from e23smtp09.au.ibm.com ([202.81.31.142]:43544 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754426Ab1D1HHh (ORCPT ); Thu, 28 Apr 2011 03:07:37 -0400 From: "Nikunj A. Dadhania" To: Nikhil Rao , Ingo Molnar , Peter Zijlstra Cc: Paul Turner , Mike Galbraith , linux-kernel@vger.kernel.org, Nikhil Rao , Srivatsa Vaddagiri , Bharata B Rao Subject: Re: [RFC][PATCH 00/18] Increase resolution of load weights In-Reply-To: <1303332697-16426-1-git-send-email-ncrao@google.com> References: <1303332697-16426-1-git-send-email-ncrao@google.com> User-Agent: Notmuch/0.3.1-59-g676d251 (http://notmuchmail.org) Emacs/23.2.1 (x86_64-redhat-linux-gnu) Date: Thu, 28 Apr 2011 12:37:27 +0530 Message-ID: MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="=-=-=" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3017 Lines: 82 --=-=-= On Wed, 20 Apr 2011 13:51:19 -0700, Nikhil Rao wrote: > Hi All, > > I have attached an early version of a RFC patchset to increase resolution of > sched entity load weights. This RFC introduces SCHED_LOAD_RESOLUTION which > scales NICE_0_LOAD by a factor of 1024. The scaling is done internally and should > be completely invisible to the user. > > Why do we need this? > This extra resolution allows us to scale on two dimensions - number of cpus and > the depth of hierarchies. It also allows for proper load balancing of low weight > task groups (for eg., nice+19 on autogroup). > > One of the big roadblocks for increasing resolution is the use of unsigned long > for load.weight, which on 32-bit architectures can overflow with ~48 max-weight > sched entities. In this RFC we convert all uses of load.weight to u64. This is > still a work-in-progress and I have listed some of the issues I am still > investigating below. > > I would like to get some feedback on the direction of this patchset. Please let > me know if there are alternative ways of doing this, and I'll be happy to > explore them as well. > > The patchset applies cleanly to v2.6.39-rc4. It compiles for i386 and boots on > x86_64. Beyond the basic checks, it has not been well tested yet. > > Major TODOs: > - Detect overflow in update shares calculations (time * load), and set load_avg > to maximum possible value (~0ULL). > - tg->task_weight uses an atomic which needs to be updates to 64-bit on 32-bit > machines. Might need to add a lock to protect this instead of atomic ops. > - Check wake-affine math and effective load calculations for overflows. > - Needs more testing and need to ensure fairness/balancing is not broken. > Hi Nikhil, I did a quick test for creating 600 cpu hog tasks with and without this patches on a 16cpu machine(x86_64) and I am seeing some mis-behaviour: Base kernel - 2.6.39-rc4 [root@krm1 ~]# time -p ./test real 43.54 user 0.12 sys 1.05 [root@krm1 ~]# Base + patches [root@krm1 ~]# time -p ./test Takes almost infinity, after 2 minutes I see only 16 tasks created viewed from another ssh session to the machine: [root@krm1 ~]# ps ax | grep dowhile$ | wc -l 16 [root@krm1 ~]# I am attaching the script. Regards, Nikunj --=-=-= Content-Type: application/x-sh Content-Disposition: attachment; filename=create_loop_tasks.sh Content-Transfer-Encoding: base64 IyEvYmluL3NoCnRvdGFsX3Rhc2tzPTYwMAppPTAKd2hpbGUgWyAkaSAtbHQgJHRvdGFsX3Rhc2tz IF0KZG8KLi9kb3doaWxlICYKaT1gZXhwciAkaSArIDFgCmRvbmUKCm51bV9kb3doaWxlPSQocHMg YXggfCBncmVwIGRvd2hpbGUkIHwgd2MgLWwpCndoaWxlIFsgJG51bV9kb3doaWxlIC1uZSAkdG90 YWxfdGFza3MgXSA7CmRvCiAgICBzbGVlcCAxCiAgICBudW1fZG93aGlsZT0kKHBzIGF4IHwgZ3Jl cCBkb3doaWxlJCB8IHdjIC1sKQpkb25lCg== --=-=-=-- -- 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/