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| author | Paul E. McKenney <paulmck@kernel.org> | 2020-03-18 17:16:37 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2020-04-27 11:03:52 -0700 |
| commit | 9ae58d7bd11f1fc4c96389df11751f8593d8bd33 (patch) | |
| tree | 2839dd92f0e5f91bedc25cd399b2a0ca619f48a1 /kernel/rcu | |
| parent | 238dbce39ea467577ce7e41ee3e98748c436ed0f (diff) | |
| download | lwn-9ae58d7bd11f1fc4c96389df11751f8593d8bd33.tar.gz lwn-9ae58d7bd11f1fc4c96389df11751f8593d8bd33.zip | |
rcu-tasks: Add Kconfig option to mediate smp_mb() vs. IPI
This commit provides a new TASKS_TRACE_RCU_READ_MB Kconfig option that
enables use of read-side memory barriers by both rcu_read_lock_trace()
and rcu_read_unlock_trace() when the are executed with the
current->trc_reader_special.b.need_mb flag set. This flag is currently
never set. Doing that is the subject of a later commit.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/Kconfig | 18 | ||||
| -rw-r--r-- | kernel/rcu/tasks.h | 3 |
2 files changed, 20 insertions, 1 deletions
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index cb1d18ef343c..0ebe15a84985 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -234,4 +234,22 @@ config RCU_NOCB_CPU Say Y here if you want to help to debug reduced OS jitter. Say N here if you are unsure. +config TASKS_TRACE_RCU_READ_MB + bool "Tasks Trace RCU readers use memory barriers in user and idle" + depends on RCU_EXPERT + default PREEMPT_RT || NR_CPUS < 8 + help + Use this option to further reduce the number of IPIs sent + to CPUs executing in userspace or idle during tasks trace + RCU grace periods. Given that a reasonable setting of + the rcupdate.rcu_task_ipi_delay kernel boot parameter + eliminates such IPIs for many workloads, proper setting + of this Kconfig option is important mostly for aggressive + real-time installations and for battery-powered devices, + hence the default chosen above. + + Say Y here if you hate IPIs. + Say N here if you hate read-side memory barriers. + Take the default if you are unsure. + endmenu # "RCU Subsystem" diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 4857450c0430..4147857007d7 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -734,7 +734,8 @@ void rcu_read_unlock_trace_special(struct task_struct *t, int nesting) { int nq = t->trc_reader_special.b.need_qs; - if (t->trc_reader_special.b.need_mb) + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && + t->trc_reader_special.b.need_mb) smp_mb(); // Pairs with update-side barriers. // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers. if (nq) |