lkml.org 
[lkml]   [2023]   [Jan]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2 rcu/dev 1/2] rcu: Track laziness during boot and suspend
Date
During boot and suspend/resume, it is desired to prevent RCU laziness from
effecting performance and in some cases failures like with suspend.

Track whether RCU laziness is to be ignored or not, in kernels with
CONFIG_RCU_LAZY enabled. We do such tracking for expedited-RCU already, however
since Android currently expedites synchronous_rcu() always, we cannot rely on
that. The next patch ignores laziness hints based on this tracking.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
Paul, could we take this and the next one for 6.2 -rc cycle?

I also booted debian Linux and verified the flag is reset correctly after boot
completes. Thanks.

kernel/rcu/rcu.h | 6 ++++++
kernel/rcu/tree.c | 2 ++
kernel/rcu/update.c | 40 +++++++++++++++++++++++++++++++++++++++-
5 files changed, 55 insertions(+), 1 deletion(-)
create mode 100644 cc_list
create mode 100644 to_list

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 5c8013f7085f..115616ac3bfa 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -449,14 +449,20 @@ do { \
/* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
static inline bool rcu_gp_is_normal(void) { return true; }
static inline bool rcu_gp_is_expedited(void) { return false; }
+static inline bool rcu_async_should_hurry(void) { return false; }
static inline void rcu_expedite_gp(void) { }
static inline void rcu_unexpedite_gp(void) { }
+static inline void rcu_async_hurry(void) { }
+static inline void rcu_async_relax(void) { }
static inline void rcu_request_urgent_qs_task(struct task_struct *t) { }
#else /* #ifdef CONFIG_TINY_RCU */
bool rcu_gp_is_normal(void); /* Internal RCU use. */
bool rcu_gp_is_expedited(void); /* Internal RCU use. */
+bool rcu_async_should_hurry(void); /* Internal RCU use. */
void rcu_expedite_gp(void);
void rcu_unexpedite_gp(void);
+void rcu_async_hurry(void);
+void rcu_async_relax(void);
void rcupdate_announce_bootup_oddness(void);
#ifdef CONFIG_TASKS_RCU_GENERIC
void show_rcu_tasks_gp_kthreads(void);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 63545d79da51..78b2e999c904 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4504,11 +4504,13 @@ static int rcu_pm_notify(struct notifier_block *self,
switch (action) {
case PM_HIBERNATION_PREPARE:
case PM_SUSPEND_PREPARE:
+ rcu_async_hurry();
rcu_expedite_gp();
break;
case PM_POST_HIBERNATION:
case PM_POST_SUSPEND:
rcu_unexpedite_gp();
+ rcu_async_relax();
break;
default:
break;
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 3893022f8ed8..19bf6fa3ee6a 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -144,8 +144,45 @@ bool rcu_gp_is_normal(void)
}
EXPORT_SYMBOL_GPL(rcu_gp_is_normal);

-static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
+static atomic_t rcu_async_hurry_nesting = ATOMIC_INIT(1);
+/*
+ * Should call_rcu() callbacks be processed with urgency or are
+ * they OK being executed with arbitrary delays?
+ */
+bool rcu_async_should_hurry(void)
+{
+ return !IS_ENABLED(CONFIG_RCU_LAZY) ||
+ atomic_read(&rcu_async_hurry_nesting);
+}
+EXPORT_SYMBOL_GPL(rcu_async_should_hurry);
+
+/**
+ * rcu_async_hurry - Make future async RCU callbacks not lazy.
+ *
+ * After a call to this function, future calls to call_rcu()
+ * will be processed in a timely fashion.
+ */
+void rcu_async_hurry(void)
+{
+ if (IS_ENABLED(CONFIG_RCU_LAZY))
+ atomic_inc(&rcu_async_hurry_nesting);
+}
+EXPORT_SYMBOL_GPL(rcu_async_hurry);

+/**
+ * rcu_async_relax - Make future async RCU callbacks lazy.
+ *
+ * After a call to this function, future calls to call_rcu()
+ * will be processed in a lazy fashion.
+ */
+void rcu_async_relax(void)
+{
+ if (IS_ENABLED(CONFIG_RCU_LAZY))
+ atomic_dec(&rcu_async_hurry_nesting);
+}
+EXPORT_SYMBOL_GPL(rcu_async_relax);
+
+static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
/*
* Should normal grace-period primitives be expedited? Intended for
* use within RCU. Note that this function takes the rcu_expedited
@@ -195,6 +232,7 @@ static bool rcu_boot_ended __read_mostly;
void rcu_end_inkernel_boot(void)
{
rcu_unexpedite_gp();
+ rcu_async_relax();
if (rcu_normal_after_boot)
WRITE_ONCE(rcu_normal, 1);
rcu_boot_ended = true;
--
2.39.0.314.g84b9a713c41-goog
\
 
 \ /
  Last update: 2023-03-26 23:37    [W:0.186 / U:0.248 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site