tree e5ad7915dac6fee31e38e9925292a13c53c5eef1
parent 5fe0a56298e674358ff2740a6288bf21509d895d
author Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1523542830 -0700
committer Paul E. McKenney <paulmck@linux.vnet.ibm.com> 1526405368 -0700

rcu: Make rcu_gp_cleanup() more accurately predict need for new GP

Currently, rcu_gp_cleanup() scans the rcu_node tree in order to reset
state to reflect the end of the grace period.  It also checks to see
whether a new grace period is needed, but in a number of cases, rather
than directly cause the new grace period to be immediately started, it
instead leaves the grace-period-needed state where various fail-safes
can find it.  This works fine, but results in higher contention on the
root rcu_node structure's ->lock, which is undesirable, and contention
on that lock has recently become noticeable.

This commit therefore makes rcu_gp_cleanup() immediately start a new
grace period if there is any need for one.

It is quite possible that it will later be necessary to throttle the
grace-period rate, but that can be dealt with when and if.

Reported-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>