From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755275AbaHUNqc (ORCPT ); Thu, 21 Aug 2014 09:46:32 -0400 Received: from mail-wi0-f180.google.com ([209.85.212.180]:35600 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754479AbaHUNqa (ORCPT ); Thu, 21 Aug 2014 09:46:30 -0400 Date: Thu, 21 Aug 2014 15:46:25 +0200 From: Ingo Molnar To: Juri Lelli Cc: peterz@infradead.org, luca.abeni@unitn.it, rdunlap@infradead.org, mingo@redhat.com, henrik@austad.us, raistlin@linux.it, juri.lelli@gmail.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/4] Documentation/scheduler/sched-deadline.txt: Rewrite section 4 intro Message-ID: <20140821134625.GB29495@gmail.com> References: <1408611700-9420-1-git-send-email-juri.lelli@arm.com> <1408611700-9420-3-git-send-email-juri.lelli@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1408611700-9420-3-git-send-email-juri.lelli@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Juri Lelli wrote: > Section 4 intro was still describing the old interface. Rewrite it. > > Signed-off-by: Juri Lelli > Signed-off-by: Luca Abeni > Cc: Randy Dunlap > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Henrik Austad > Cc: Dario Faggioli > Cc: Juri Lelli > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > --- > Documentation/scheduler/sched-deadline.txt | 49 +++++++++++++++--------------- > 1 file changed, 24 insertions(+), 25 deletions(-) > > diff --git a/Documentation/scheduler/sched-deadline.txt b/Documentation/scheduler/sched-deadline.txt > index dce6d63..8372c3d 100644 > --- a/Documentation/scheduler/sched-deadline.txt > +++ b/Documentation/scheduler/sched-deadline.txt > @@ -165,39 +165,38 @@ CONTENTS > > In order for the -deadline scheduling to be effective and useful, it is > important to have some method to keep the allocation of the available CPU > - bandwidth to the tasks under control. > - This is usually called "admission control" and if it is not performed at all, > - no guarantee can be given on the actual scheduling of the -deadline tasks. > - > - Since when RT-throttling has been introduced each task group has a bandwidth > - associated, calculated as a certain amount of runtime over a period. > - Moreover, to make it possible to manipulate such bandwidth, readable/writable > - controls have been added to both procfs (for system wide settings) and cgroupfs > - (for per-group settings). > - Therefore, the same interface is being used for controlling the bandwidth > - distrubution to -deadline tasks. > - > - However, more discussion is needed in order to figure out how we want to manage > - SCHED_DEADLINE bandwidth at the task group level. Therefore, SCHED_DEADLINE > - uses (for now) a less sophisticated, but actually very sensible, mechanism to > - ensure that a certain utilization cap is not overcome per each root_domain. > - > - Another main difference between deadline bandwidth management and RT-throttling > + bandwidth to the tasks under control. This is usually called "admission > + control" and if it is not performed at all, no guarantee can be given on > + the actual scheduling of the -deadline tasks. > + > + The interface used to control the fraction of CPU bandwidth that can be > + allocated to -deadline tasks is similar to the one already used for -rt > + tasks with real-time group scheduling (a.k.a. RT-throttling - see > + Documentation/scheduler/sched-rt-group.txt), and is based on readable/ > + writable control files located in procfs (for system wide settings). > + Notice that per-group settings (controlled through cgroupfs) are still not > + defined for -deadline tasks, because more discussion is needed in order to > + figure out how we want to manage SCHED_DEADLINE bandwidth at the task group > + level. > + > + A main difference between deadline bandwidth management and RT-throttling > is that -deadline tasks have bandwidth on their own (while -rt ones don't!), > and thus we don't need an higher level throttling mechanism to enforce the s/an higher/a higher > - desired bandwidth. > + desired bandwidth. Therefore, using this simple interface, we can put a cap s/interface, we/interface we > + on total utilization of -deadline tasks (i.e., \Sum (runtime_i / period_i) < > + some_desired_value). Thanks, Ingo