linux-kernel - Re: [PATCH RFC] sched: Micro optimization in pick_next_task() and in check_preempt

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Date:   Thu, 19 Dec 2019 09:43:30 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] sched: Micro optimization in pick_next_task() and
 in check_preempt_curr()

On Thu, 19 Dec 2019 17:25:40 +0300
Kirill Tkhai <ktkhai@...tuozzo.com> wrote:

> (17:19:25) nbjoerg: but it is not guarenteed behavior
> (17:19:50) nbjoerg: if for some strange reason you really need to enforce relative orders of global objects, put them in consecutively named sections

Which appears to work. I tried this patch on top of yours:

Not sure how this does with locality though.

-- Steve

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e00f41aa8ec4..ff12a422ff19 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -108,6 +108,13 @@
 #define SBSS_MAIN .sbss
 #endif
 
+#define SCHED_DATA				\
+	*(__idle_sched_class)			\
+	*(__fair_sched_class)			\
+	*(__rt_sched_class)			\
+	*(__dl_sched_class)			\
+	*(__stop_sched_class)
+
 /*
  * Align to a 32 byte boundary equal to the
  * alignment gcc 4.5 uses for a struct
@@ -308,6 +315,7 @@
 #define DATA_DATA							\
 	*(.xiptext)							\
 	*(DATA_MAIN)							\
+	SCHED_DATA							\
 	*(.ref.data)							\
 	*(.data..shared_aligned) /* percpu related */			\
 	MEM_KEEP(init.data*)						\
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 43323f875cb9..5abdbe569f93 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2428,7 +2428,8 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
 	}
 }
 
-const struct sched_class dl_sched_class = {
+const struct sched_class dl_sched_class
+	__attribute__((section("__dl_sched_class"))) = {
 	.next			= &rt_sched_class,
 	.enqueue_task		= enqueue_task_dl,
 	.dequeue_task		= dequeue_task_dl,
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 08a233e97a01..e745fe0e0cd3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10745,7 +10745,8 @@ static unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task
 /*
  * All the scheduling class methods:
  */
-const struct sched_class fair_sched_class = {
+const struct sched_class fair_sched_class
+	__attribute__((section("__fair_sched_class"))) = {
 	.next			= &idle_sched_class,
 	.enqueue_task		= enqueue_task_fair,
 	.dequeue_task		= dequeue_task_fair,
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index ffa959e91227..700a9c826f0e 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -454,7 +454,8 @@ static void update_curr_idle(struct rq *rq)
 /*
  * Simple, special scheduling class for the per-CPU idle tasks:
  */
-const struct sched_class idle_sched_class = {
+const struct sched_class idle_sched_class
+	__attribute__((section("__idle_sched_class"))) = {
 	/* .next is NULL */
 	/* no enqueue/yield_task for idle tasks */
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index e591d40fd645..5d3f9bcddaeb 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2354,7 +2354,8 @@ static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
 		return 0;
 }
 
-const struct sched_class rt_sched_class = {
+const struct sched_class rt_sched_class
+	__attribute__((section("__rt_sched_class"))) = {
 	.next			= &fair_sched_class,
 	.enqueue_task		= enqueue_task_rt,
 	.dequeue_task		= dequeue_task_rt,
diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
index 4c9e9975684f..03bc7530ff75 100644
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -115,7 +115,8 @@ static void update_curr_stop(struct rq *rq)
 /*
  * Simple, special scheduling class for the per-CPU stop tasks:
  */
-const struct sched_class stop_sched_class = {
+const struct sched_class stop_sched_class
+	__attribute__((section("__stop_sched_class"))) = {
 	.next			= &dl_sched_class,
 
 	.enqueue_task		= enqueue_task_stop,