linux-kernel - [PATCH v2 0/1] Touch kernel watchdog with sched count

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Date:   Tue, 20 Oct 2020 13:57:03 -0700
From:   Xi Wang <xii@...gle.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Don <joshdon@...gle.com>, linux-kernel@...r.kernel.org,
        Xi Wang <xii@...gle.com>
Subject: [PATCH v2 0/1] Touch kernel watchdog with sched count

The main purpose of kernel watchdog is to test whether scheduler can
still schedule tasks on a cpu. In order to reduce latency / jitter
from periodically invoking watchdog reset in thread context, we can
simply test if pick_next_task can run. This is done by forcing resched
and checking rq->sched_count. Compared to actually resetting watchdog
from cpu stop / migration threads, we lose coverage on: a migration
thread actually get picked and we actually context switch to the
migration thread. These steps are unlikely to silently fail. The
change would provide nearly the same level of protection with less
overhead.

With this patch we can still switch back to the old method with the
boot option watchdog_touch_with_thread. However code for the old
method can be completely removed in the future.

v2:
 - Use sched_count instead of having sched calling into watchdog code
 - Remove the sysctl and add a boot option, which can be removed later
 - Changed the subject line

Xi Wang (1):
  sched: watchdog: Touch kernel watchdog with sched count

 include/linux/sched.h |  4 ++++
 kernel/sched/core.c   | 23 ++++++++++++++++++++--
 kernel/sched/sched.h  |  6 +++++-
 kernel/watchdog.c     | 44 +++++++++++++++++++++++++++++++++++++------
 4 files changed, 68 insertions(+), 9 deletions(-)

-- 
2.29.0.rc1.297.gfa9743e501-goog