From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751936AbeBAKxw (ORCPT ); Thu, 1 Feb 2018 05:53:52 -0500 Received: from mail-wr0-f193.google.com ([209.85.128.193]:45478 "EHLO mail-wr0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751748AbeBAKxu (ORCPT ); Thu, 1 Feb 2018 05:53:50 -0500 X-Google-Smtp-Source: AH8x2267H8hC+g0AwjzHAJro9ieeJclNgVOrY8wAuGFKcJVzkoMtJ9ItL3SRXY9FwL7plrERHPEVJQ== Date: Thu, 1 Feb 2018 11:53:45 +0100 From: Juri Lelli To: Daniel Bristot de Oliveira Cc: Jonathan Corbet , Luca Abeni , Tommaso Cucinotta , Claudio Scordino , Peter Zijlstra , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] Documentation/scheduler/sched-rt-group: Update SCHED DEADLINE references Message-ID: <20180201105345.GG19535@localhost.localdomain> References: <61a3d8b77457f71452294d0aba371674e4ec7693.1517480458.git.bristot@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <61a3d8b77457f71452294d0aba371674e4ec7693.1517480458.git.bristot@redhat.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Daniel, On 01/02/18 11:31, Daniel Bristot de Oliveira wrote: > The documentation was mentioning the "future SCHED EDF" as the > solution for fine-grained control of deadline/period. This patch > updates this citing the (now) existing SCHED_DEADLINE. > > Signed-off-by: Daniel Bristot de Oliveira > Cc: Jonathan Corbet > Cc: Juri Lelli > Cc: Luca Abeni > Cc: Tommaso Cucinotta > Cc: Claudio Scordino > Cc: Peter Zijlstra > Cc: linux-doc@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > > --- > Documentation/scheduler/sched-rt-group.txt | 19 +++++-------------- > 1 file changed, 5 insertions(+), 14 deletions(-) > > diff --git a/Documentation/scheduler/sched-rt-group.txt b/Documentation/scheduler/sched-rt-group.txt > index d8fce3e78457..ed763c243914 100644 > --- a/Documentation/scheduler/sched-rt-group.txt > +++ b/Documentation/scheduler/sched-rt-group.txt > @@ -153,7 +153,7 @@ There is work in progress to make the scheduling period for each group > > The constraint on the period is that a subgroup must have a smaller or > equal period to its parent. But realistically its not very useful _yet_ > -as its prone to starvation without deadline scheduling. > +as its prone to starvation. > > Consider two sibling groups A and B; both have 50% bandwidth, but A's > period is twice the length of B's. > @@ -168,16 +168,7 @@ This means that currently a while (1) loop in A will run for the full period of > B and can starve B's tasks (assuming they are of lower priority) for a whole > period. > > -The next project will be SCHED_EDF (Earliest Deadline First scheduling) to bring > -full deadline scheduling to the linux kernel. Deadline scheduling the above > -groups and treating end of the period as a deadline will ensure that they both > -get their allocated time. > - > -Implementing SCHED_EDF might take a while to complete. Priority Inheritance is > -the biggest challenge as the current linux PI infrastructure is geared towards > -the limited static priority levels 0-99. With deadline scheduling you need to > -do deadline inheritance (since priority is inversely proportional to the > -deadline delta (deadline - now)). > - > -This means the whole PI machinery will have to be reworked - and that is one of > -the most complex pieces of code we have. > +Nowadays it is possible to use the deadline scheduler (SCHED_DEADLINE) to > +allocate runtime/period for tasks. The deadline scheduler does not suffer the > +side effects explained above. For more information about the deadline > +scheduler, you should read Documentation/scheduler/sched-deadline.txt. True. But it doesn't have support for groups yet (while this doc seems to refer to groups). Maybe add a paragraph about this? Thanks, - Juri