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From:   Chengming Zhou <zhouchengming@bytedance.com>
To:     hannes@cmpxchg.org, mingo@redhat.com, peterz@infradead.org,
        juri.lelli@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org
Cc:     linux-kernel@vger.kernel.org, songmuchun@bytedance.com,
        zhouchengming@bytedance.com
Subject: [PATCH v2 3/4] psi: pressure states are unlikely
Date:   Wed,  3 Mar 2021 11:46:58 +0800
Message-Id: <20210303034659.91735-4-zhouchengming@bytedance.com>
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From: Johannes Weiner <hannes@cmpxchg.org>

Move the unlikely branches out of line. This eliminates undesirable
jumps during wakeup and sleeps for workloads that aren't under any
sort of resource pressure.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 kernel/sched/psi.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 0fe6ff6a6a15..3907a6b847aa 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -219,17 +219,17 @@ static bool test_state(unsigned int *tasks, enum psi_states state)
 {
 	switch (state) {
 	case PSI_IO_SOME:
-		return tasks[NR_IOWAIT];
+		return unlikely(tasks[NR_IOWAIT]);
 	case PSI_IO_FULL:
-		return tasks[NR_IOWAIT] && !tasks[NR_RUNNING];
+		return unlikely(tasks[NR_IOWAIT] && !tasks[NR_RUNNING]);
 	case PSI_MEM_SOME:
-		return tasks[NR_MEMSTALL];
+		return unlikely(tasks[NR_MEMSTALL]);
 	case PSI_MEM_FULL:
-		return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING];
+		return unlikely(tasks[NR_MEMSTALL] && !tasks[NR_RUNNING]);
 	case PSI_CPU_SOME:
-		return tasks[NR_RUNNING] > tasks[NR_ONCPU];
+		return unlikely(tasks[NR_RUNNING] > tasks[NR_ONCPU]);
 	case PSI_CPU_FULL:
-		return tasks[NR_RUNNING] && !tasks[NR_ONCPU];
+		return unlikely(tasks[NR_RUNNING] && !tasks[NR_ONCPU]);
 	case PSI_NONIDLE:
 		return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
 			tasks[NR_RUNNING];
@@ -729,7 +729,7 @@ static void psi_group_change(struct psi_group *group, int cpu,
 	 * task in a cgroup is in_memstall, the corresponding groupc
 	 * on that cpu is in PSI_MEM_FULL state.
 	 */
-	if (groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall)
+	if (unlikely(groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall))
 		state_mask |= (1 << PSI_MEM_FULL);
 
 	groupc->state_mask = state_mask;
-- 
2.11.0