From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752193AbeBAKcZ (ORCPT ); Thu, 1 Feb 2018 05:32:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40972 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751766AbeBAKcV (ORCPT ); Thu, 1 Feb 2018 05:32:21 -0500 From: Daniel Bristot de Oliveira To: Jonathan Corbet Cc: Juri Lelli , Luca Abeni , Tommaso Cucinotta , Claudio Scordino , Peter Zijlstra , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] Documentation/scheduler/sched-rt-group: Update SCHED DEADLINE references Date: Thu, 1 Feb 2018 11:31:59 +0100 Message-Id: <61a3d8b77457f71452294d0aba371674e4ec7693.1517480458.git.bristot@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- 2.14.3