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From: 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 06/10] srcu: Document polling interfaces for Tree SRCU grace periods
Date: Wed,  6 Jan 2021 08:55:27 -0800
Message-ID: <20210106165531.20697-6-paulmck@kernel.org> (raw)
In-Reply-To: <20210106165511.GA20555@paulmck-ThinkPad-P72>

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit adds requirements documentation for the
get_state_synchronize_srcu(), start_poll_synchronize_srcu(), and
poll_state_synchronize_srcu() functions.

Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/
Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 Documentation/RCU/Design/Requirements/Requirements.rst | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
index e8c84fc..93a189a 100644
--- a/Documentation/RCU/Design/Requirements/Requirements.rst
+++ b/Documentation/RCU/Design/Requirements/Requirements.rst
@@ -2600,6 +2600,24 @@ also includes ``DEFINE_SRCU()``, ``DEFINE_STATIC_SRCU()``, and
 ``init_srcu_struct()`` APIs for defining and initializing
 ``srcu_struct`` structures.
 
+More recently, the SRCU API has added polling interfaces:
+
+#. start_poll_synchronize_srcu() returns a cookie identifying
+   the completion of a future SRCU grace period and ensures
+   that this grace period will be started.
+#. poll_state_synchronize_srcu() returns ``true`` iff the
+   specified cookie corresponds to an already-completed
+   SRCU grace period.
+#. get_state_synchronize_srcu() returns a cookie just like
+   start_poll_synchronize_srcu() does, but differs in that
+   it does nothing to ensure that any future SRCU grace period
+   will be started.
+
+These functions are used to avoid unnecessary SRCU grace periods in
+certain types of buffer-cache algorithms having multi-stage age-out
+mechanisms.  The idea is that by the time the block has aged completely
+from the cache, an SRCU grace period will be very likely to have elapsed.
+
 Tasks RCU
 ~~~~~~~~~
 
-- 
2.9.5


  parent reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-06 16:55 [PATCH tip/core/rcu 0/10] SRCU updates for v5.12 Paul E. McKenney
2021-01-06 16:55 ` [PATCH tip/core/rcu 01/10] srcu: Make Tiny SRCU use multi-bit grace-period counter paulmck
2021-01-06 16:55 ` [PATCH tip/core/rcu 02/10] srcu: Provide internal interface to start a Tiny SRCU grace period paulmck
2021-01-06 16:55 ` [PATCH tip/core/rcu 03/10] srcu: Provide internal interface to start a Tree " paulmck
2021-01-06 16:55 ` [PATCH tip/core/rcu 04/10] srcu: Provide polling interfaces for Tiny SRCU grace periods paulmck
2021-01-06 16:55 ` [PATCH tip/core/rcu 05/10] srcu: Provide polling interfaces for Tree " paulmck
2021-01-06 16:55 ` paulmck [this message]
2021-01-06 16:55 ` [PATCH tip/core/rcu 07/10] srcu: Add comment explaining cookie overflow/wrap paulmck
2021-01-06 16:55 ` [PATCH tip/core/rcu 08/10] rcutorture: Prepare for ->start_gp_poll and ->poll_gp_state paulmck
2021-01-06 16:55 ` [PATCH tip/core/rcu 09/10] rcutorture: Add writer-side tests of polling grace-period API paulmck
2021-01-06 16:55 ` [PATCH tip/core/rcu 10/10] rcutorture: Add reader-side " paulmck

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