Messages in this thread | | | From | "Zhang, Qiang1" <> | Subject | RE: [PATCH] rcu: Only boost rcu reader tasks with lower priority than boost kthreads | Date | Mon, 7 Mar 2022 02:03:17 +0000 |
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On 3/4/2022 2:56 PM, Zqiang wrote: > When RCU_BOOST is enabled, the boost kthreads will boosting readers > who are blocking a given grace period, if the current reader tasks > have a higher priority than boost kthreads(the boost kthreads priority > not always 1, if the kthread_prio is set), boosting is useless, skip > current task and select next task to boosting, reduce the time for a > given grace period. > > Signed-off-by: Zqiang <qiang1.zhang@intel.com> > --- > kernel/rcu/tree_plugin.h | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index c3d212bc5338..d35b6da66bbd 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -12,6 +12,7 @@ > */ > > #include "../locking/rtmutex_common.h" > +#include <linux/sched/deadline.h> > > static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) > { > @@ -1065,13 +1066,20 @@ static int rcu_boost(struct rcu_node *rnp) > * section. > */ > t = container_of(tb, struct task_struct, rcu_node_entry); > + if (!rnp->exp_tasks && (dl_task(t) || t->prio <= current->prio)) { > + tb = rcu_next_node_entry(t, rnp); > + WRITE_ONCE(rnp->boost_tasks, tb); > + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > + goto end; > + } > + > rt_mutex_init_proxy_locked(&rnp->boost_mtx.rtmutex, t); > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > /* Lock only for side effect: boosts task t's priority. */ > rt_mutex_lock(&rnp->boost_mtx); > rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ > rnp->n_boosts++; > - > +end: >> >>Nit: maybe rename the label to "skip_boost:" ? >> >>Code looks fine; however, out of curiosity; given that the higher >>priority tasks, in general, would exit their read side critical section >>quickly and boost the next blocking reader on exiting their read side >>section; do you see noticeable reduction in grace period timings with >>the change for certain type of workloads?
Thanks for feedback , In preempt-RT systems, there will be many real-time threads (most of them are created by users themselves ), their priority is higher or lower than boost kthreads (kthread_prio is set), for rt tasks with higher priority than boost kthreads, maybe it will exit read side critical quickly, maybe not, if it is preempted by a higher priority task, If try to boost operation, this increases the boosts kthread waiting time, as a result, the next blkd tasks cannot be boosted in time. of course, I don't deny it, there are also reasons that user priority setting is inappropriate.
Thanks Zqiang
>> >> >>Thanks >>Neeraj
> return READ_ONCE(rnp->exp_tasks) != NULL || > READ_ONCE(rnp->boost_tasks) != NULL; > }
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