From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756239AbcA2PGO (ORCPT ); Fri, 29 Jan 2016 10:06:14 -0500 Received: from casper.infradead.org ([85.118.1.10]:37704 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751825AbcA2PGM (ORCPT ); Fri, 29 Jan 2016 10:06:12 -0500 Date: Fri, 29 Jan 2016 16:06:05 +0100 From: Peter Zijlstra To: Luca Abeni Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Juri Lelli Subject: Re: [RFC 5/8] Track the "total rq utilisation" too Message-ID: <20160129150605.GA2906@worktop> References: <1452785094-3086-1-git-send-email-luca.abeni@unitn.it> <1452785094-3086-6-git-send-email-luca.abeni@unitn.it> <20160114194837.GE6357@twins.programming.kicks-ass.net> <20160115075049.1e24bde8@luca-1225C> <20160115083359.GC3421@worktop> <20160115101511.726cfe29@luca-1225C> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160115101511.726cfe29@luca-1225C> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 15, 2016 at 10:15:11AM +0100, Luca Abeni wrote: > There is also a newer paper, that will be published at ACM SAC 2016 > (so, it is not available yet), but is based on this technical report: > http://arxiv.org/abs/1512.01984 > This second paper describes some more complex algorithms (easily > implementable over this patchset) that are able to guarantee hard > schedulability for SCHED_DEADLINE tasks with reclaiming on SMP. So I finally got around to reading the relevant sections of that paper (5.1 and 5.2). The paper introduces two alternatives; - parallel reclaim (5.1) - sequential reclaim (5.2) The parent patch introduces the accounting required for sequential reclaiming IIUC. Thinking about things however, I think I would prefer parallel reclaim over sequential reclaim. The problem I see with sequential reclaim is that under light load jobs might land on different CPUs and not benefit from reclaim (as much) since the 'spare' bandwidth is stuck on other CPUs. Now I suppose the exact conditions to hit that worst case might be quite hard to trigger, in which case it might just not matter in practical terms. But maybe I'm mistaken, the paper doesn't seem to compare the two approaches in this way.