Messages in this thread | | | Date | Wed, 6 Sep 2023 10:44:55 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 1/2] sched: Rate limit migrations to 1 per 2ms per task |
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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.
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