linux-kernel - [PATCH 2/4] sched/core: change rq->nr_iowait type to atomic_long

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Date: Tue, 16 Apr 2024 06:11:19 -0600
From: Jens Axboe <axboe@...nel.dk>
To: linux-kernel@...r.kernel.org
Cc: peterz@...radead.org,
	tglx@...utronix.de,
	Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 2/4] sched/core: change rq->nr_iowait type to atomic_long_t on 64-bit

In preparation for storing two separate iowait states in there, bump the
size from a 32-bit to a 64-bit size, for 64-bit kernels.

Note that on 32-bit, the number of tasks are limited to 0x8000, which
fits just fine in even half of the existiing 32-bit atomic_t. For 64-bit,
no such limit exists, hence play it safe and make it a 64-bit atomic.

Signed-off-by: Jens Axboe <axboe@...nel.dk>
---
 kernel/sched/core.c  | 14 +++++++++++++-
 kernel/sched/sched.h |  4 ++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 977bb08a33d2..6a6c985220b1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3723,17 +3723,29 @@ static inline cpumask_t *alloc_user_cpus_ptr(int node)
 
 static void task_iowait_inc(struct task_struct *p)
 {
+#ifdef CONFIG_64BIT
+	atomic_long_inc(&task_rq(p)->nr_iowait);
+#else
 	atomic_inc(&task_rq(p)->nr_iowait);
+#endif
 }
 
 static void task_iowait_dec(struct task_struct *p)
 {
+#ifdef CONFIG_64BIT
+	atomic_long_dec(&task_rq(p)->nr_iowait);
+#else
 	atomic_dec(&task_rq(p)->nr_iowait);
+#endif
 }
 
 int rq_iowait(struct rq *rq)
 {
+#ifdef CONFIG_64BIT
+	return atomic_long_read(&rq->nr_iowait);
+#else
 	return atomic_read(&rq->nr_iowait);
+#endif
 }
 
 static void
@@ -10065,7 +10077,7 @@ void __init sched_init(void)
 #endif
 #endif /* CONFIG_SMP */
 		hrtick_rq_init(rq);
-		atomic_set(&rq->nr_iowait, 0);
+		atomic_long_set(&rq->nr_iowait, 0);
 
 #ifdef CONFIG_SCHED_CORE
 		rq->core = rq;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 387f67ddf18a..c2802d066615 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1049,7 +1049,11 @@ struct rq {
 	u64			clock_idle_copy;
 #endif
 
+#ifdef CONFIG_64BIT
+	atomic_long_t		nr_iowait;
+#else
 	atomic_t		nr_iowait;
+#endif
 
 #ifdef CONFIG_SCHED_DEBUG
 	u64 last_seen_need_resched_ns;
-- 
2.43.0