From: Qais Yousef <qyousef@layalina.io>
To: "Paul E. McKenney" <paulmck@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>
Cc: Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>,
Josh Triplett <josh@joshtriplett.org>,
Boqun Feng <boqun.feng@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang1211@gmail.com>,
Andrea Righi <andrea.righi@canonical.com>,
John Stultz <jstultz@google.com>,
linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
Qais Yousef <qyousef@layalina.io>
Subject: [PATCH v2] rcu: Provide a boot time parameter to control lazy RCU
Date: Sun, 3 Dec 2023 01:12:52 +0000 [thread overview]
Message-ID: <20231203011252.233748-1-qyousef@layalina.io> (raw)
To allow more flexible arrangements while still provide a single kernel
for distros, provide a boot time parameter to enable/disable lazy RCU.
Specify:
rcutree.enable_rcu_lazy=[y|1|n|0]
Which also requires
rcu_nocbs=all
at boot time to enable/disable lazy RCU.
To disable it by default at build time when CONFIG_RCU_LAZY=y, the new
CONFIG_RCU_LAZY_DEFAULT_OFF can be used.
Signed-off-by: Qais Yousef (Google) <qyousef@layalina.io>
---
Changes since v1:
* Use module_param() instead of module_param_cb()
* Add new CONFIG_RCU_LAZY_DEFAULT_OFF to force default off.
* Remove unnecessary READ_ONCE()
Tested on qemu only this time with various config/boot configuration to ensure
expected values are in sysfs.
Did a bunch of build tests against various configs/archs.
Documentation/admin-guide/kernel-parameters.txt | 5 +++++
kernel/rcu/Kconfig | 13 +++++++++++++
kernel/rcu/tree.c | 7 ++++++-
3 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 65731b060e3f..2f0386a12aa7 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5021,6 +5021,11 @@
this kernel boot parameter, forcibly setting it
to zero.
+ rcutree.enable_rcu_lazy= [KNL]
+ To save power, batch RCU callbacks and flush after
+ delay, memory pressure or callback list growing too
+ big.
+
rcuscale.gp_async= [KNL]
Measure performance of asynchronous
grace-period primitives such as call_rcu().
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index bdd7eadb33d8..e7d2dd267593 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -314,6 +314,19 @@ config RCU_LAZY
To save power, batch RCU callbacks and flush after delay, memory
pressure, or callback list growing too big.
+ Requires rcu_nocbs=all to be set.
+
+ Use rcutree.enable_rcu_lazy=0 to turn it off at boot time.
+
+config RCU_LAZY_DEFAULT_OFF
+ bool "Turn RCU lazy invocation off by default"
+ depends on RCU_LAZY
+ default n
+ help
+ Allows building the kernel with CONFIG_RCU_LAZY=y yet keep it default
+ off. Boot time param rcutree.enable_rcu_lazy=1 can be used to switch
+ it back on.
+
config RCU_DOUBLE_CHECK_CB_TIME
bool "RCU callback-batch backup time check"
depends on RCU_EXPERT
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3ac3c846105f..8b7675624815 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2719,6 +2719,9 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
}
#ifdef CONFIG_RCU_LAZY
+static bool enable_rcu_lazy __read_mostly = !IS_ENABLED(CONFIG_RCU_LAZY_DEFAULT_OFF);
+module_param(enable_rcu_lazy, bool, 0444);
+
/**
* call_rcu_hurry() - Queue RCU callback for invocation after grace period, and
* flush all lazy callbacks (including the new one) to the main ->cblist while
@@ -2744,6 +2747,8 @@ void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
__call_rcu_common(head, func, false);
}
EXPORT_SYMBOL_GPL(call_rcu_hurry);
+#else
+#define enable_rcu_lazy false
#endif
/**
@@ -2792,7 +2797,7 @@ EXPORT_SYMBOL_GPL(call_rcu_hurry);
*/
void call_rcu(struct rcu_head *head, rcu_callback_t func)
{
- __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY));
+ __call_rcu_common(head, func, enable_rcu_lazy);
}
EXPORT_SYMBOL_GPL(call_rcu);
--
2.34.1
next reply other threads:[~2023-12-03 1:13 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-03 1:12 Qais Yousef [this message]
2023-12-03 13:18 ` [PATCH v2] rcu: Provide a boot time parameter to control lazy RCU Andrea Righi
2023-12-05 4:27 ` Paul E. McKenney
2023-12-05 16:20 ` Joel Fernandes
2023-12-07 17:20 ` Qais Yousef
2023-12-09 6:26 ` Joel Fernandes
2023-12-12 12:05 ` Qais Yousef
2023-12-12 22:32 ` Joel Fernandes
2023-12-12 12:35 ` Uladzislau Rezki
2023-12-12 22:28 ` Joel Fernandes
2023-12-13 10:35 ` Uladzislau Rezki
2023-12-15 16:32 ` Joel Fernandes
2023-12-15 16:58 ` Uladzislau Rezki
2023-12-15 18:46 ` Paul E. McKenney
2023-12-15 22:47 ` Joel Fernandes
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=20231203011252.233748-1-qyousef@layalina.io \
--to=qyousef@layalina.io \
--cc=andrea.righi@canonical.com \
--cc=boqun.feng@gmail.com \
--cc=frederic@kernel.org \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=jstultz@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=paulmck@kernel.org \
--cc=qiang.zhang1211@gmail.com \
--cc=quic_neeraju@quicinc.com \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).