From: "Paul E. McKenney" <paulmck@kernel.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>
Subject: Re: [RFC PATCH 10/12] rcu: Process batch locally as long as offloading isn't complete
Date: Mon, 21 Sep 2020 17:22:15 -0700 [thread overview]
Message-ID: <20200922002214.GQ29330@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200921124351.24035-11-frederic@kernel.org>
On Mon, Sep 21, 2020 at 02:43:49PM +0200, Frederic Weisbecker wrote:
> During the offloading or de-offloading process, make sure to process
> the callbacks batch locally whenever the segcblist isn't entirely
> offloaded. This enforces callback service processing while we are still
> in intermediate (de-)offloading state.
>
> FIXME: Note that __call_rcu_core() isn't called during these intermediate
> states. Some pieces there may still be necessary.
Joel's per-segment callback-count work might help there, though I believe
that to be a separate issue.
The key point is that if there are a lot of callbacks, but all of them
are ready to be invoked, then there isn't much point in making the
grace periods complete faster. Right now, lacking per-segment counts,
RCU just assumes that none of the callbacks are ready to be invoked.
Thanx, Paul
> Inspired-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Cc: Lai Jiangshan <jiangshanlai@gmail.com>
> Cc: Joel Fernandes <joel@joelfernandes.org>
> ---
> kernel/rcu/rcu_segcblist.h | 12 ++++++++++++
> kernel/rcu/tree.c | 3 ++-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
> index 00ebeb8d39b7..f7da3d535888 100644
> --- a/kernel/rcu/rcu_segcblist.h
> +++ b/kernel/rcu/rcu_segcblist.h
> @@ -92,6 +92,18 @@ static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
> return false;
> }
>
> +static inline bool rcu_segcblist_completely_offloaded(struct rcu_segcblist *rsclp)
> +{
> + int flags = SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP | SEGCBLIST_OFFLOADED;
> +
> + if (IS_ENABLED(CONFIG_RCU_NOCB_CPU)) {
> + if ((rsclp->flags & flags) == flags)
> + return true;
> + }
> +
> + return false;
> +}
> +
> /*
> * Are all segments following the specified segment of the specified
> * rcu_segcblist structure empty of callbacks? (The specified
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index b4292489db0c..928907e9ba94 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2620,6 +2620,7 @@ static __latent_entropy void rcu_core(void)
> struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
> struct rcu_node *rnp = rdp->mynode;
> const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
> + const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
>
> if (cpu_is_offline(smp_processor_id()))
> return;
> @@ -2649,7 +2650,7 @@ static __latent_entropy void rcu_core(void)
> rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
>
> /* If there are callbacks ready, invoke them. */
> - if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist) &&
> + if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
> likely(READ_ONCE(rcu_scheduler_fully_active)))
> rcu_do_batch(rdp);
>
> --
> 2.28.0
>
next prev parent reply other threads:[~2020-09-22 0:22 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-21 12:43 [RFC PATCH 00/12] rcu/nocb: De-offload and re-offload support v2 Frederic Weisbecker
2020-09-21 12:43 ` [RFC PATCH 01/12] rcu: Implement rcu_segcblist_is_offloaded() config dependent Frederic Weisbecker
2020-09-22 0:27 ` Paul E. McKenney
2020-09-22 21:43 ` Frederic Weisbecker
2020-09-22 23:11 ` Paul E. McKenney
2020-09-23 15:25 ` Frederic Weisbecker
2020-09-21 12:43 ` [RFC PATCH 02/12] rcu: Turn enabled/offload states into a common flag Frederic Weisbecker
2020-09-21 12:43 ` [RFC PATCH 03/12] rcu: Provide basic callback offloading state machine bits Frederic Weisbecker
2020-09-21 23:50 ` Paul E. McKenney
2020-09-21 12:43 ` [RFC PATCH 04/12] rcu: De-offloading CB kthread Frederic Weisbecker
2020-09-22 0:07 ` Paul E. McKenney
2020-09-21 12:43 ` [RFC PATCH 05/12] rcu: De-offloading GP kthread Frederic Weisbecker
2020-09-22 0:10 ` Paul E. McKenney
2020-09-23 15:31 ` Frederic Weisbecker
2020-09-23 15:48 ` Paul E. McKenney
2020-09-21 12:43 ` [RFC PATCH 06/12] rcu: Re-offload support Frederic Weisbecker
2020-09-21 12:43 ` [RFC PATCH 07/12] rcu: Shutdown nocb timer on de-offloading Frederic Weisbecker
2020-09-22 0:17 ` Paul E. McKenney
2020-09-23 15:29 ` Frederic Weisbecker
2020-09-23 15:47 ` Paul E. McKenney
2020-09-21 12:43 ` [RFC PATCH 08/12] rcu: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY Frederic Weisbecker
2020-09-21 12:43 ` [RFC PATCH 09/12] rcu: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading Frederic Weisbecker
2020-09-21 12:43 ` [RFC PATCH 10/12] rcu: Process batch locally as long as offloading isn't complete Frederic Weisbecker
2020-09-22 0:22 ` Paul E. McKenney [this message]
2020-09-21 12:43 ` [RFC PATCH 11/12] rcu: Locally accelerate callbacks " Frederic Weisbecker
2020-09-22 0:24 ` Paul E. McKenney
2020-09-21 12:43 ` [RFC PATCH 12/12] rcu: Nocb (de)activate through sysfs Frederic Weisbecker
2020-09-22 0:26 ` Paul E. McKenney
2020-09-23 15:27 ` Frederic Weisbecker
2020-09-23 15:47 ` Paul E. McKenney
2020-09-23 19:00 ` Frederic Weisbecker
2020-09-24 0:38 ` Paul E. McKenney
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