linux-kernel - [PATCH 0/2] Fix DEADLINE bandwidth accounting in root domain changes and hotplug

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Message-ID: <20241113125724.450249-1-juri.lelli@redhat.com>
Date: Wed, 13 Nov 2024 12:57:21 +0000
From: Juri Lelli <juri.lelli@...hat.com>
To: Waiman Long <longman@...hat.com>,
	Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutny <mkoutny@...e.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>
Cc: Qais Yousef <qyousef@...alina.io>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	"Joel Fernandes (Google)" <joel@...lfernandes.org>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Aashish Sharma <shraash@...gle.com>,
	Shin Kawamura <kawasin@...gle.com>,
	Vineeth Remanan Pillai <vineeth@...byteword.org>,
	linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org,
	Juri Lelli <juri.lelli@...hat.com>
Subject: [PATCH 0/2] Fix DEADLINE bandwidth accounting in root domain changes and hotplug

Hello!

This patch series addresses two issues affecting DEADLINE bandwidth
accounting during non-destructive changes to root domains and hotplug
operations. The series is based on top of Waiman's "cgroup/cpuset:
Remove redundant rebuild_sched_domains_locked() calls" series [1] which
is now merged into cgroups/for-6.13 (this series is based on top of
that, commit c4c9cebe2fb9). The discussion that eventually led to these
two series can be found at [2].

Patch 01/02 deals with non-destructive root domain changes. Currently,
such operations do not correctly account for dl_server contributions, as
they are only considered on destructive changes (where runqueues are
reattached to new domains). This patch ensures that dl_servers’
bandwidth contributions are properly re-added to root domains that
remain unchanged, preventing accounting discrepancies.

Patch 02/02 deals with hotplug. For CPU hotplug events, DEADLINE
bandwidth needs verification to ensure adequate bandwidth remains after
a CPU goes offline. The current implementation overlooks this check,
potentially leading to overflow conditions. This patch modifies
dl_bw_manage() to correctly detect and handle overflow situations,
special casing dl_servers' bandwidth contibution.

Please go forth and test/review.

Series also available at

git@...hub.com:jlelli/linux.git upstream/dl-server-apply

Best,
Juri

[1] https://lore.kernel.org/lkml/20241110025023.664487-1-longman@redhat.com/
[2] https://lore.kernel.org/lkml/20241029225116.3998487-1-joel@joelfernandes.org/

Juri Lelli (2):
  sched/deadline: Restore dl_server bandwidth on non-destructive root
    domain changes
  sched/deadline: Correctly account for allocated bandwidth during
    hotplug

 include/linux/sched/deadline.h |  2 +-
 kernel/cgroup/cpuset.c         |  2 +-
 kernel/sched/core.c            |  2 +-
 kernel/sched/deadline.c        | 51 ++++++++++++++++++++++++----------
 kernel/sched/sched.h           |  2 +-
 kernel/sched/topology.c        | 10 ++++---
 6 files changed, 47 insertions(+), 22 deletions(-)

-- 
2.47.0