From: Neeraj Upadhyay <quic_neeraju@quicinc.com>
To: Zqiang <qiang1.zhang@intel.com>, <paulmck@kernel.org>,
<frederic@kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] rcu: Only boost rcu reader tasks with lower priority than boost kthreads
Date: Fri, 4 Mar 2022 17:12:36 +0530 [thread overview]
Message-ID: <81f69dd4-6ca9-760c-bec5-5cb27afbe788@quicinc.com> (raw)
In-Reply-To: <20220304092631.4123188-1-qiang1.zhang@intel.com>
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
Neeraj
> return READ_ONCE(rnp->exp_tasks) != NULL ||
> READ_ONCE(rnp->boost_tasks) != NULL;
> }
next prev parent reply other threads:[~2022-03-04 11:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-04 9:26 [PATCH] rcu: Only boost rcu reader tasks with lower priority than boost kthreads Zqiang
2022-03-04 11:42 ` Neeraj Upadhyay [this message]
2022-03-07 2:03 ` Zhang, Qiang1
2022-03-07 19:15 ` Paul E. McKenney
2022-03-08 18:04 ` Uladzislau Rezki
2022-03-08 18:13 ` Paul E. McKenney
2022-03-08 18:25 ` Uladzislau Rezki
2022-03-09 3:04 ` Zhang, Qiang1
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