linux-kernel - Should RCU_BOOST kernels use hrtimers in GP kthread?

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Message-ID: <20210216183609.GA7027@paulmck-ThinkPad-P72>
Date:   Tue, 16 Feb 2021 10:36:09 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     bigeasy@...utronix.de
Cc:     linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Subject: Should RCU_BOOST kernels use hrtimers in GP kthread?

Hello, Sebastian,

I punted on this for the moment by making RCU priority boosting testing
depend on CONFIG_PREEMPT_RT, but longer term I am wondering if RCU's
various timed delays and timeouts should use hrtimers rather than normal
timers in kernels built with CONFIG_RCU_BOOST.  As it is, RCU priority
boosting can be defeated if any of the RCU grace-period kthread's timeouts
are serviced by the non-realtime ksoftirqd.

This might require things like swait_event_idle_hrtimeout_exclusive(),
either as primitives or just open coded.

Thoughts?

							Thanx, Paul