linux-kernel - [tip: sched/core] sched/fair: Dissociate wakeup decisions from SD flag value

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Date:   Wed, 11 Nov 2020 08:23:12 -0000
From:   "tip-bot2 for Valentin Schneider" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Valentin Schneider <valentin.schneider@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/fair: Dissociate wakeup decisions from SD flag value

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     dc824eb898534cd8e34582874dae3bb7cf2fa008
Gitweb:        https://git.kernel.org/tip/dc824eb898534cd8e34582874dae3bb7cf2fa008
Author:        Valentin Schneider <valentin.schneider@....com>
AuthorDate:    Mon, 02 Nov 2020 18:45:14 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 10 Nov 2020 18:39:06 +01:00

sched/fair: Dissociate wakeup decisions from SD flag value

The CFS wakeup code will only ever go through EAS / its fast path on
"regular" wakeups (i.e. not on forks or execs). These are currently gated
by a check against 'sd_flag', which would be SD_BALANCE_WAKE at wakeup.

However, we now have a flag that explicitly tells us whether a wakeup is a
"regular" one, so hinge those conditions on that flag instead.

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20201102184514.2733-4-valentin.schneider@arm.com
---
 kernel/sched/fair.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b1596fa..6691e28 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6705,7 +6705,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 	/* SD_flags and WF_flags share the first nibble */
 	int sd_flag = wake_flags & 0xF;
 
-	if (sd_flag & SD_BALANCE_WAKE) {
+	if (wake_flags & WF_TTWU) {
 		record_wakee(p);
 
 		if (sched_energy_enabled()) {
@@ -6742,9 +6742,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags)
 	if (unlikely(sd)) {
 		/* Slow path */
 		new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
-	} else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
+	} else if (wake_flags & WF_TTWU) { /* XXX always ? */
 		/* Fast path */
-
 		new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
 
 		if (want_affine)