From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 1/4] rcu-tasks: Add block comment laying out RCU Tasks design
Date: Tue, 11 May 2021 16:09:39 -0700 [thread overview]
Message-ID: <20210511230942.2894861-1-paulmck@kernel.org> (raw)
In-Reply-To: <20210511230720.GA2894512@paulmck-ThinkPad-P17-Gen-1>
This commit adds a block comment that gives a high-level overview of how
RCU tasks grace periods progress. It also adds a note about how exiting
tasks are handled, plus it gives an overview of the memory ordering.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tasks.h | 40 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 350ebf5051f9..94d2c2c7f0ab 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -377,6 +377,46 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
// Finally, this implementation does not support high call_rcu_tasks()
// rates from multiple CPUs. If this is required, per-CPU callback lists
// will be needed.
+//
+// The implementation uses rcu_tasks_wait_gp(), which relies on function
+// pointers in the rcu_tasks structure. The rcu_spawn_tasks_kthread()
+// function sets these function pointers up so that rcu_tasks_wait_gp()
+// invokes these functions in this order:
+//
+// rcu_tasks_pregp_step():
+// Invokes synchronize_rcu() in order to wait for all in-flight
+// t->on_rq and t->nvcsw transitions to complete. This works because
+// all such transitions are carried out with interrupts disabled.
+// rcu_tasks_pertask(), invoked on every non-idle task:
+// For every runnable non-idle task other than the current one, use
+// get_task_struct() to pin down that task, snapshot that task's
+// number of voluntary context switches, and add that task to the
+// holdout list.
+// rcu_tasks_postscan():
+// Invoke synchronize_srcu() to ensure that all tasks that were
+// in the process of exiting (and which thus might not know to
+// synchronize with this RCU Tasks grace period) have completed
+// exiting.
+// check_all_holdout_tasks(), repeatedly until holdout list is empty:
+// Scans the holdout list, attempting to identify a quiescent state
+// for each task on the list. If there is a quiescent state, the
+// corresponding task is removed from the holdout list.
+// rcu_tasks_postgp():
+// Invokes synchronize_rcu() in order to ensure that all prior
+// t->on_rq and t->nvcsw transitions are seen by all CPUs and tasks
+// to have happened before the end of this RCU Tasks grace period.
+// Again, this works because all such transitions are carried out
+// with interrupts disabled.
+//
+// For each exiting task, the exit_tasks_rcu_start() and
+// exit_tasks_rcu_finish() functions begin and end, respectively, the SRCU
+// read-side critical sections waited for by rcu_tasks_postscan().
+//
+// Pre-grace-period update-side code is ordered before the grace via the
+// ->cbs_lock and the smp_mb__after_spinlock(). Pre-grace-period read-side
+// code is ordered before the grace period via synchronize_rcu() call
+// in rcu_tasks_pregp_step() and by the scheduler's locks and interrupt
+// disabling.
/* Pre-grace-period preparation. */
static void rcu_tasks_pregp_step(void)
--
2.31.1.189.g2e36527f23
next prev parent reply other threads:[~2021-05-11 23:09 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 23:07 [PATCH tip/core/rcu 0/6] SRCU updates for v5.14 Paul E. McKenney
2021-05-11 23:07 ` [PATCH tip/core/rcu 1/6] srcu: Remove superfluous sdp->srcu_lock_count zero filling Paul E. McKenney
2021-05-11 23:07 ` [PATCH tip/core/rcu 2/6] srcu: Remove superfluous ssp initialization for early callbacks Paul E. McKenney
2021-05-11 23:07 ` [PATCH tip/core/rcu 3/6] srcu: Unconditionally embed struct lockdep_map Paul E. McKenney
2021-05-11 23:07 ` [PATCH tip/core/rcu 4/6] srcu: Initialize SRCU after timers Paul E. McKenney
2021-05-11 23:07 ` [PATCH tip/core/rcu 5/6] srcu: Fix broken node geometry after early ssp init Paul E. McKenney
2021-05-11 23:07 ` [PATCH tip/core/rcu 6/6] srcu: Early test SRCU polling start Paul E. McKenney
2021-05-11 23:09 ` Paul E. McKenney [this message]
2021-05-11 23:09 ` [PATCH tip/core/rcu 2/4] rcu-tasks: Add block comment laying out RCU Rude design Paul E. McKenney
2021-05-11 23:09 ` [PATCH tip/core/rcu 3/4] rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states Paul E. McKenney
2021-05-11 23:09 ` [PATCH tip/core/rcu 4/4] tasks-rcu: Make show_rcu_tasks_gp_kthreads() be static inline Paul E. McKenney
-- strict thread matches above, loose matches on Subject: below --
2021-05-12 18:27 [PATCH tip/core/rcu 1/4] rcu-tasks: Add block comment laying out RCU Tasks design Paul E. McKenney
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210511230942.2894861-1-paulmck@kernel.org \
--to=paulmck@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=dhowells@redhat.com \
--cc=edumazet@google.com \
--cc=fweisbec@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.