LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Luca Abeni <luca.abeni@unitn.it>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@gmail.com>,
	Dario Faggioli <raistlin@linux.it>,
	linux-kernel@vger.kernel.org, luca.abeni@unitn.it
Subject: [PATCH 1/2] Fix migration of SCHED_DEADLINE tasks
Date: Wed, 17 Dec 2014 11:50:31 +0100
Message-ID: <1418813432-20797-2-git-send-email-luca.abeni@unitn.it> (raw)
In-Reply-To: <1418813432-20797-1-git-send-email-luca.abeni@unitn.it>

According to global EDF, tasks should be migrated between runqueues
without checking if their scheduling deadlines and runtimes are valid.
However, SCHED_DEADLINE currently performs such a check:
a migration happens doing
	deactivate_task(rq, next_task, 0);
	set_task_cpu(next_task, later_rq->cpu);
	activate_task(later_rq, next_task, 0);
which ends up calling dequeue_task_dl(), setting the new CPU, and then
calling enqueue_task_dl().
enqueue_task_dl() then calls enqueue_dl_entity(), which calls
update_dl_entity(), which can modify scheduling deadline and runtime,
breaking global EDF scheduling.
As a result, some of the properties of global EDF are not respected:
for example, a taskset {(30, 80), (40, 80), (120, 170)} scheduled on
two cores can have unbounded response times for the third task even
if 30/80+40/80+120/170 = 1.5809 < 2

This can be fixed by invoking update_dl_entity() only in case of
wakeup, or if this is a new SCHED_DEADLINE task.

Signed-off-by: Luca Abeni <luca.abeni@unitn.it>
---
 kernel/sched/deadline.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index e5db8c6..55af498 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -826,10 +826,10 @@ enqueue_dl_entity(struct sched_dl_entity *dl_se,
 	 * parameters of the task might need updating. Otherwise,
 	 * we want a replenishment of its runtime.
 	 */
-	if (!dl_se->dl_new && flags & ENQUEUE_REPLENISH)
-		replenish_dl_entity(dl_se, pi_se);
-	else
+	if (dl_se->dl_new || flags & ENQUEUE_WAKEUP)
 		update_dl_entity(dl_se, pi_se);
+	else if (flags & ENQUEUE_REPLENISH)
+		replenish_dl_entity(dl_se, pi_se);
 
 	__enqueue_dl_entity(dl_se);
 }
-- 
1.9.1


  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-17 10:50 [PATCH 0/2] SCHED_DEADLINE fixes Luca Abeni
2014-12-17 10:50 ` Luca Abeni [this message]
2015-01-09 12:33   ` [tip:sched/urgent] sched/deadline: Fix migration of SCHED_DEADLINE tasks tip-bot for Luca Abeni
2014-12-17 10:50 ` [PATCH 2/2] Avoid double-accounting in case of missed deadlines Luca Abeni
2015-01-09 12:34   ` [tip:sched/urgent] sched/deadline: " tip-bot for Luca Abeni
2014-12-17 12:49 ` [PATCH 0/2] SCHED_DEADLINE fixes Juri Lelli

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1418813432-20797-2-git-send-email-luca.abeni@unitn.it \
    --to=luca.abeni@unitn.it \
    --cc=juri.lelli@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=raistlin@linux.it \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git