linux-kernel - [PATCH 5/5] x86/percpu, sched/fair: Avoid local

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Date:   Wed, 27 Feb 2019 11:12:57 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     torvalds@...ux-foundation.org, mingo@...nel.org, bp@...en8.de,
        tglx@...utronix.de, luto@...nel.org, namit@...are.com,
        peterz@...radead.org
Cc:     linux-kernel@...r.kernel.org, Nadav Amit <nadav.amit@...il.com>
Subject: [PATCH 5/5] x86/percpu, sched/fair: Avoid local_clock()

Nadav reported that code-gen changed because of the this_cpu_*()
constraints, avoid this for select_idle_cpu() because that runs with
preemption (and IRQs) disabled anyway.

Reported-by: Nadav Amit <nadav.amit@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/fair.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6160,6 +6160,7 @@ static int select_idle_cpu(struct task_s
 	u64 time, cost;
 	s64 delta;
 	int cpu, nr = INT_MAX;
+	int this = smp_processor_id();
 
 	this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
 	if (!this_sd)
@@ -6183,7 +6184,7 @@ static int select_idle_cpu(struct task_s
 			nr = 4;
 	}
 
-	time = local_clock();
+	time = cpu_clock(this);
 
 	for_each_cpu_wrap(cpu, sched_domain_span(sd), target) {
 		if (!--nr)
@@ -6194,7 +6195,7 @@ static int select_idle_cpu(struct task_s
 			break;
 	}
 
-	time = local_clock() - time;
+	time = cpu_clock(this) - time;
 	cost = this_sd->avg_scan_cost;
 	delta = (s64)(time - cost) / 8;
 	this_sd->avg_scan_cost += delta;