tree cd7a9bfdde0086ddff1949bb783add6357c494d4
parent 2c85ebc57b3e1817b6ce1a6b703928e113a90442
author Paul E. McKenney <paulmck@kernel.org> 1666667034 -0700
committer Paul E. McKenney <paulmck@kernel.org> 1666667034 -0700

rcu: Let non-offloaded idle CPUs with callbacks defer tick

When a CPU goes idle, rcu_needs_cpu() is invoked to determine whether or
not RCU needs the scheduler-clock tick to keep interrupting.  Right now,
RCU keeps the tick on for a given idle CPU if there are any non-offloaded
callbacks queued on that CPU.

But if all of these callbacks are waiting for a grace period to finish,
there is no point in scheduling a tick before that grace period has any
reasonable chance of completing.  This commit therefore delays the tick
in the case where all the callbacks are waiting for a specific grace
period to elapse.  In theory, this should result in a 50-70% reduction in
RCU-induced scheduling-clock ticks on mostly-idle CPUs.  In practice, TBD.
/bin/bash: fm: command not found

Backported from -rcu commit 0de11f7d3589 ("rcu: Let non-offloaded idle
CPUs with callbacks defer tick").

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Joel Fernandes <joel@joelfernandes.org>

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>