Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752740AbdCXV6u (ORCPT ); Fri, 24 Mar 2017 17:58:50 -0400 Received: from mail.santannapisa.it ([193.205.80.99]:47010 "EHLO mail.santannapisa.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752436AbdCXV6m (ORCPT ); Fri, 24 Mar 2017 17:58:42 -0400 Date: Fri, 24 Mar 2017 22:58:27 +0100 From: luca abeni To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Juri Lelli , Claudio Scordino , Steven Rostedt , Tommaso Cucinotta , Daniel Bristot de Oliveira , Joel Fernandes , Mathieu Poirier Subject: Re: [RFC v5 5/9] sched/deadline: do not reclaim the whole CPU bandwidth Message-ID: <20170324225827.402a4f20@nowhere> In-Reply-To: <20170324140015.fptmmtqynvjy723q@hirez.programming.kicks-ass.net> References: <1490327582-4376-1-git-send-email-luca.abeni@santannapisa.it> <1490327582-4376-6-git-send-email-luca.abeni@santannapisa.it> <20170324140015.fptmmtqynvjy723q@hirez.programming.kicks-ass.net> Organization: Scuola Superiore S.Anna X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2225 Lines: 88 Hi Peter, On Fri, 24 Mar 2017 15:00:15 +0100 Peter Zijlstra wrote: > On Fri, Mar 24, 2017 at 04:52:58AM +0100, luca abeni wrote: > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index 20c62e7..efa88eb 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -6716,6 +6716,12 @@ static void sched_dl_do_global(void) > > raw_spin_unlock_irqrestore(&dl_b->lock, flags); > > > > rcu_read_unlock_sched(); > > + if (dl_b->bw == -1) > > + cpu_rq(cpu)->dl.deadline_bw_inv = 1 << 8; > > + else > > + cpu_rq(cpu)->dl.deadline_bw_inv = > > + to_ratio(global_rt_runtime(), > > + global_rt_period()) >> > > 12; > > Coding style requires braces here (on both legs of the condition).. Sorry about this; checkpatch did not complain and I did not check the coding rules. I'll add the braces. > Also, I find deadline_bw_inv an awkward name; would something like > bw_ratio or so be more accurate? I am not good at finding names :) (I used "deadline_bw_inv" because it represents the inverse of the deadline tasks bandwidth") I'll change the name in bw_ratio or something better (suggestions?) > > + if (global_rt_runtime() == RUNTIME_INF) > > + dl_rq->deadline_bw_inv = 1 << 8; > > + else > > + dl_rq->deadline_bw_inv = > > + to_ratio(global_rt_runtime(), > > global_rt_period()) >> 12; > > That's almost the same code; do we want a helper function? OK, I'll look at this. > > u64 grub_reclaim(u64 delta, struct rq *rq) > > { > > + return (delta * rq->dl.running_bw * > > rq->dl.deadline_bw_inv) >> 20 >> 8; } > > At which point we might want a note about how this doesn't overflow I > suppose. I'll add it on Monday. > > Also: > > delta *= rq->dl.running_bw; > delta *= rq->dl.bw_ratio; > delta >>= 20 + 8; > > return delta; > > Might be more readable ? > > Alternatively: > > delta = (delta * rq->dl.running_bw) >> 8; > delta = (delta * rq->dl.bw_ratio) >> 20; > > return delta; > > But I doubt we care about those extra 8 bit of space; delta should not > be over 36 bits (~64 seconds) anyway I suppose. I think the version with all the shifts after the multiplications is more precise, right? Thanks, Luca