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From cc7c761946c6b9fa820acc90d7514795af3f42f5 Mon Sep 17 00:00:00 2001
From: jplozi <jplozi@unice.fr>
Date: Fri, 11 Mar 2016 15:18:06 +0100
Subject: [PATCH 111/126] overload on wakeup
source https://github.com/jplozi/wastedcores
as an experiment, apply the learnings from the wasted-cores paper
and see how the performance works out. With the data from this we should
be able to work with Peter and the rest of the scheduler folks on
a more permanent/elegant solution.
---
kernel/sched/fair.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
--- linux-4.14/kernel/sched/fair.c.org 2017-11-18 23:01:57.353611850 +0000
+++ linux-4.14/kernel/sched/fair.c 2017-11-19 15:24:38.093637926 +0000
@@ -5925,6 +5925,8 @@
return min_cap * 1024 < task_util(p) * capacity_margin;
}
+
+static unsigned int once_in_a_while;
/*
* select_task_rq_fair: Select target runqueue for the waking task in domains
* that have the 'sd_flag' flag set. In practice, this is SD_BALANCE_WAKE,
@@ -5953,6 +5955,30 @@
}
rcu_read_lock();
+
+ once_in_a_while++;
+
+ if (cpu_rq(prev_cpu)->nr_running || (once_in_a_while & 15) == 0) {
+ int _cpu;
+ int bestprio = -5000;
+ int bestcpu = -1;
+
+ for_each_online_cpu(_cpu) {
+ if (!cpumask_test_cpu(_cpu, &p->cpus_allowed) ||
+ cpu_rq(_cpu)->nr_running)
+ continue;
+ if (arch_asym_cpu_priority(_cpu) > bestprio || (prev_cpu == _cpu && bestprio == arch_asym_cpu_priority(_cpu))) {
+ bestcpu = _cpu;
+ bestprio = arch_asym_cpu_priority(_cpu);
+ }
+ }
+
+ if (bestcpu > 0) {
+ rcu_read_unlock();
+ return bestcpu;
+ }
+ }
+
for_each_domain(cpu, tmp) {
if (!(tmp->flags & SD_LOAD_BALANCE))
break;
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