linux-kernel - [RFC][PATCH 0/5] sched: Diagnostic checks for missing rq clock updates

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Message-Id: <1463082593-27777-1-git-send-email-matt@codeblueprint.co.uk>
Date:	Thu, 12 May 2016 20:49:48 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Byungchul Park <byungchul.park@....com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Luca Abeni <luca.abeni@...tn.it>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wanpeng Li <wanpeng.li@...mail.com>,
	Yuyang Du <yuyang.du@...el.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: [RFC][PATCH 0/5] sched: Diagnostic checks for missing rq clock updates

There are currently no runtime diagnostic checks for detecting when we
have inadvertently missed a call to update_rq_clock() before accessing
rq_clock().

The idea in these patches, which came from Peter, is to piggyback on
the rq->lock pin/unpin context to detect when we expected (and failed)
to see an update to the rq clock. They've already caught a couple of
bugs: see patch 1 and commit b52fad2db5d7 ("sched/fair: Update rq
clock before updating nohz CPU load") in tip/sched/core.

I'm not sure how palatable the s/pin_cookie/rq_flags/ changes will be
in patch 2, so I've marked this entire series as RFC.

All the diagnostic code is guarded by CONFIG_SCHED_DEBUG, but there
are minimal changes to __schedule() in patch 5 for the !SCHED_DEBUG
case.

Matt Fleming (5):
  sched/fair: Update the rq clock before detaching tasks
  sched: Add wrappers for lockdep_(un)pin_lock()
  sched/core: Reset RQCF_ACT_SKIP before unpinning rq->lock
  sched/fair: Push rq lock pin/unpin into idle_balance()
  sched/core: Add debug code to catch missing update_rq_clock()

 kernel/sched/core.c      |  94 +++++++++++++++++++++++--------------------
 kernel/sched/deadline.c  |  10 ++---
 kernel/sched/fair.c      |  31 +++++++++------
 kernel/sched/idle_task.c |   2 +-
 kernel/sched/rt.c        |   6 +--
 kernel/sched/sched.h     | 101 ++++++++++++++++++++++++++++++++++++++++-------
 kernel/sched/stop_task.c |   2 +-
 7 files changed, 166 insertions(+), 80 deletions(-)

-- 
2.7.3