On Tue, Sep 05, 2023 at 05:16:25PM -0400, Mathieu Desnoyers wrote:
On 9/5/23 16:28, Tim Chen wrote:
On Tue, 2023-09-05 at 13:11 -0400, Mathieu Desnoyers wrote:
Rate limit migrations to 1 migration per 2 milliseconds per task. On a
kernel with EEVDF scheduler (commit b97d64c722598ffed42ece814a2cb791336c6679),
this speeds up hackbench from 62s to 45s on AMD EPYC 192-core (over 2 sockets).
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 479db611f46e..0d294fce261d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4510,6 +4510,7 @@ static void __sched_fork(unsigned long clone_flags, struct task_struct *p)
p->se.vruntime = 0;
p->se.vlag = 0;
p->se.slice = sysctl_sched_base_slice;
+ p->se.next_migration_time = 0;
It seems like the next_migration_time should be initialized to the current time,
in case the system run for a long time and clock wrap around could cause problem.
next_migration_time is a u64, which should "never" overflow. Other scheduler
code comparing with sched_clock() don't appear to care about u64 overflow.
Much code actually considers overflow. We also have monotonicity filters
where it really matters.