From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E . McKenney" <paulmck@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Boqun Feng <boqun.feng@gmail.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>,
rcu@vger.kernel.org
Subject: [PATCH 02/19] rcu/nocb: Provide basic callback offloading state machine bits
Date: Fri, 13 Nov 2020 13:13:17 +0100 [thread overview]
Message-ID: <20201113121334.166723-3-frederic@kernel.org> (raw)
In-Reply-To: <20201113121334.166723-1-frederic@kernel.org>
We'll need to be able to runtime offload and de-offload the processing
of callback for a given CPU. In order to support a smooth transition
from unlocked local processing (softirq/rcuc) to locked offloaded
processing (rcuop/rcuog) and the reverse, provide the necessary bits and
documentation for the state machine that will carry up all the steps to
enforce correctness while serving callbacks processing all along.
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>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
---
include/linux/rcu_segcblist.h | 115 +++++++++++++++++++++++++++++++++-
kernel/rcu/rcu_segcblist.c | 1 +
kernel/rcu/rcu_segcblist.h | 12 +++-
kernel/rcu/tree.c | 3 +
4 files changed, 128 insertions(+), 3 deletions(-)
diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h
index 4714b0263c76..4ca08b089faf 100644
--- a/include/linux/rcu_segcblist.h
+++ b/include/linux/rcu_segcblist.h
@@ -63,8 +63,121 @@ struct rcu_cblist {
#define RCU_NEXT_TAIL 3
#define RCU_CBLIST_NSEGS 4
+
+/*
+ * ==NOCB Offloading state machine==
+ *
+ *
+ * ----------------------------------------------------------------------------
+ * | SEGCBLIST_SOFTIRQ_ONLY |
+ * | |
+ * | Callbacks processed by rcu_core() from softirqs or local |
+ * | rcuc kthread, without holding nocb_lock. |
+ * ----------------------------------------------------------------------------
+ * |
+ * v
+ * ----------------------------------------------------------------------------
+ * | SEGCBLIST_OFFLOADED |
+ * | |
+ * | Callbacks processed by rcu_core() from softirqs or local |
+ * | rcuc kthread, while holding nocb_lock. Waking up CB and GP kthreads, |
+ * | allowing nocb_timer to be armed. |
+ * ----------------------------------------------------------------------------
+ * |
+ * v
+ * -----------------------------------
+ * | |
+ * v v
+ * --------------------------------------- ----------------------------------|
+ * | SEGCBLIST_OFFLOADED | | | SEGCBLIST_OFFLOADED | |
+ * | SEGCBLIST_KTHREAD_CB | | SEGCBLIST_KTHREAD_GP |
+ * | | | |
+ * | | | |
+ * | CB kthread woke up and | | GP kthread woke up and |
+ * | acknowledged SEGCBLIST_OFFLOADED. | | acknowledged SEGCBLIST_OFFLOADED|
+ * | Processes callbacks concurrently | | |
+ * | with rcu_core(), holding | | |
+ * | nocb_lock. | | |
+ * --------------------------------------- -----------------------------------
+ * | |
+ * -----------------------------------
+ * |
+ * v
+ * |--------------------------------------------------------------------------|
+ * | SEGCBLIST_OFFLOADED | |
+ * | SEGCBLIST_KTHREAD_CB | |
+ * | SEGCBLIST_KTHREAD_GP |
+ * | |
+ * | Kthreads handle callbacks holding nocb_lock, local rcu_core() stops |
+ * | handling callbacks. |
+ * ----------------------------------------------------------------------------
+ */
+
+
+
+/*
+ * ==NOCB De-Offloading state machine==
+ *
+ *
+ * |--------------------------------------------------------------------------|
+ * | SEGCBLIST_OFFLOADED | |
+ * | SEGCBLIST_KTHREAD_CB | |
+ * | SEGCBLIST_KTHREAD_GP |
+ * | |
+ * | CB/GP kthreads handle callbacks holding nocb_lock, local rcu_core() |
+ * | ignores callbacks. |
+ * ----------------------------------------------------------------------------
+ * |
+ * v
+ * |--------------------------------------------------------------------------|
+ * | SEGCBLIST_KTHREAD_CB | |
+ * | SEGCBLIST_KTHREAD_GP |
+ * | |
+ * | CB/GP kthreads and local rcu_core() handle callbacks concurrently |
+ * | holding nocb_lock. Wake up CB and GP kthreads if necessary. |
+ * ----------------------------------------------------------------------------
+ * |
+ * v
+ * -----------------------------------
+ * | |
+ * v v
+ * ---------------------------------------------------------------------------|
+ * | |
+ * | SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP |
+ * | | |
+ * | GP kthread woke up and | CB kthread woke up and |
+ * | acknowledged the fact that | acknowledged the fact that |
+ * | SEGCBLIST_OFFLOADED got cleared. | SEGCBLIST_OFFLOADED got cleared. |
+ * | | The CB kthread goes to sleep |
+ * | The callbacks from the target CPU | until it ever gets re-offloaded. |
+ * | will be ignored from the GP kthread | |
+ * | loop. | |
+ * ----------------------------------------------------------------------------
+ * | |
+ * -----------------------------------
+ * |
+ * v
+ * ----------------------------------------------------------------------------
+ * | 0 |
+ * | |
+ * | Callbacks processed by rcu_core() from softirqs or local |
+ * | rcuc kthread, while holding nocb_lock. Forbid nocb_timer to be armed. |
+ * | Flush pending nocb_timer. Flush nocb bypass callbacks. |
+ * ----------------------------------------------------------------------------
+ * |
+ * v
+ * ----------------------------------------------------------------------------
+ * | SEGCBLIST_SOFTIRQ_ONLY |
+ * | |
+ * | Callbacks processed by rcu_core() from softirqs or local |
+ * | rcuc kthread, without holding nocb_lock. |
+ * ----------------------------------------------------------------------------
+ */
#define SEGCBLIST_ENABLED BIT(0)
-#define SEGCBLIST_OFFLOADED BIT(1)
+#define SEGCBLIST_SOFTIRQ_ONLY BIT(1)
+#define SEGCBLIST_KTHREAD_CB BIT(2)
+#define SEGCBLIST_KTHREAD_GP BIT(3)
+#define SEGCBLIST_OFFLOADED BIT(4)
struct rcu_segcblist {
struct rcu_head *head;
diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c
index e374f9c3ec2c..d7cb9dc044ea 100644
--- a/kernel/rcu/rcu_segcblist.c
+++ b/kernel/rcu/rcu_segcblist.c
@@ -254,6 +254,7 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
*/
void rcu_segcblist_offload(struct rcu_segcblist *rsclp)
{
+ rcu_segcblist_clear_flags(rsclp, SEGCBLIST_SOFTIRQ_ONLY);
rcu_segcblist_set_flags(rsclp, SEGCBLIST_OFFLOADED);
}
diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index 3d1195dbf030..70e108c0e7c9 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -80,8 +80,16 @@ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
/* Is the specified rcu_segcblist offloaded? */
static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
{
- return IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
- rcu_segcblist_test_flags(rsclp, SEGCBLIST_OFFLOADED);
+ if (IS_ENABLED(CONFIG_RCU_NOCB_CPU)) {
+ /*
+ * Complete de-offloading happens only when SEGCBLIST_SOFTIRQ_ONLY
+ * is set.
+ */
+ if (!rcu_segcblist_test_flags(rsclp, SEGCBLIST_SOFTIRQ_ONLY))
+ return true;
+ }
+
+ return false;
}
/*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 413831b48648..48e8e63cdeb2 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -83,6 +83,9 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
.dynticks_nesting = 1,
.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
.dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
+#ifdef CONFIG_RCU_NOCB_CPU
+ .cblist.flags = SEGCBLIST_SOFTIRQ_ONLY,
+#endif
};
static struct rcu_state rcu_state = {
.level = { &rcu_state.node[0] },
--
2.25.1
next prev parent reply other threads:[~2020-11-13 12:15 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-13 12:13 [PATCH 00/19] rcu/nocb: De-offload and re-offload support v4 Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 01/19] rcu/nocb: Turn enabled/offload states into a common flag Frederic Weisbecker
2020-11-13 12:13 ` Frederic Weisbecker [this message]
2020-11-13 12:13 ` [PATCH 03/19] rcu/nocb: Always init segcblist on CPU up Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 04/19] rcu/nocb: De-offloading CB kthread Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 05/19] rcu/nocb: Don't deoffload an offline CPU with pending work Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 06/19] rcu/nocb: De-offloading GP kthread Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 07/19] rcu/nocb: Re-offload support Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 08/19] rcu/nocb: Shutdown nocb timer on de-offloading Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 09/19] rcu: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 10/19] rcu/nocb: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 11/19] rcu/nocb: Only cond_resched() from actual offloaded batch processing Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 12/19] rcu/nocb: Process batch locally as long as offloading isn't complete Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 13/19] rcu/nocb: Locally accelerate callbacks " Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 14/19] tools/rcutorture: Support nocb toggle in TREE01 Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 15/19] rcutorture: Remove weak nocb declarations Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 16/19] rcutorture: Export nocb (de)offloading functions Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 17/19] cpu/hotplug: Add lockdep_is_cpus_held() Frederic Weisbecker
2020-12-15 23:49 ` Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 18/19] timer: Add timer_curr_running() Frederic Weisbecker
2020-11-13 12:13 ` [PATCH 19/19] rcu/nocb: Detect unsafe checks for offloaded rdp Frederic Weisbecker
2020-11-13 17:35 ` kernel test robot
2020-12-08 2:41 ` [PATCH 00/19] rcu/nocb: De-offload and re-offload support v4 Boqun Feng
2020-12-08 12:51 ` Frederic Weisbecker
2020-12-10 1:21 ` Paul E. McKenney
2020-12-10 3:08 ` Boqun Feng
2020-12-16 16:59 ` Paul E. McKenney
2020-12-29 14:21 ` Frederic Weisbecker
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=20201113121334.166723-3-frederic@kernel.org \
--to=frederic@kernel.org \
--cc=boqun.feng@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=neeraju@codeaurora.org \
--cc=paulmck@kernel.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.