diff options
| author | Sebastian Andrzej Siewior | 2019-03-20 22:13:33 +0100 |
|---|---|---|
| committer | Paul E. McKenney | 2019-05-25 14:50:46 -0700 |
| commit | 48d07c04b4cc1dc1221965312f58fd84926212fe (patch) | |
| tree | f70300d26abc17bca3602990cca44f309a2120af /Documentation/admin-guide | |
| parent | a188339ca5a396acc588e5851ed7e19f66b0ebd9 (diff) | |
rcu: Enable elimination of Tree-RCU softirq processing
Some workloads need to change kthread priority for RCU core processing
without affecting other softirq work. This commit therefore introduces
the rcutree.use_softirq kernel boot parameter, which moves the RCU core
work from softirq to a per-CPU SCHED_OTHER kthread named rcuc. Use of
SCHED_OTHER approach avoids the scalability problems that appeared
with the earlier attempt to move RCU core processing to from softirq
to kthreads. That said, kernels built with RCU_BOOST=y will run the
rcuc kthreads at the RCU-boosting priority.
Note that rcutree.use_softirq=0 must be specified to move RCU core
processing to the rcuc kthreads: rcutree.use_softirq=1 is the default.
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ paulmck: Adjust for invoke_rcu_callbacks() only ever being invoked
from RCU core processing, in contrast to softirq->rcuc transition
in old mainline RCU priority boosting. ]
[ paulmck: Avoid wakeups when scheduler might have invoked rcu_read_unlock()
while holding rq or pi locks, also possibly fixing a pre-existing latent
bug involving raise_softirq()-induced wakeups. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'Documentation/admin-guide')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 138f6664b2e2..b96fd15c7316 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3752,6 +3752,12 @@ the propagation of recent CPU-hotplug changes up the rcu_node combining tree. + rcutree.use_softirq= [KNL] + If set to zero, move all RCU_SOFTIRQ processing to + per-CPU rcuc kthreads. Defaults to a non-zero + value, meaning that RCU_SOFTIRQ is used by default. + Specify rcutree.use_softirq=0 to use rcuc kthreads. + rcutree.rcu_fanout_exact= [KNL] Disable autobalancing of the rcu_node combining tree. This is used by rcutorture, and might |