From ebb064aa22715ae473f72468d093e7a05e3c3c58 Mon Sep 17 00:00:00 2001 From: Dario Faggioli Date: Wed, 17 Apr 2013 10:57:30 +0000 Subject: [PATCH] xen: sched_credit: when picking, make sure we get an idle one, if any The pcpu picking algorithm treats two threads of a SMT core the same. More specifically, if one is idle and the other one is busy, they both will be assigned a weight of 1. Therefore, when picking begins, if the first target pcpu is the busy thread (and if there are no other idle pcpu than its sibling), that will never change. This change fixes this by ensuring that, before entering the core of the picking algorithm, the target pcpu is an idle one (if there is an idle pcpu at all, of course). Signed-off-by: Dario Faggioli Acked-by: Juergen Gross Acked-by: George Dunlap Acked-by: Keir Fraser --- xen/common/sched_credit.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c index 9e9ef33a49..64e76c5bef 100644 --- a/xen/common/sched_credit.c +++ b/xen/common/sched_credit.c @@ -532,6 +532,21 @@ _csched_cpu_pick(const struct scheduler *ops, struct vcpu *vc, bool_t commit) if ( vc->processor == cpu && IS_RUNQ_IDLE(cpu) ) cpumask_set_cpu(cpu, &idlers); cpumask_and(&cpus, &cpus, &idlers); + + /* + * It is important that cpu points to an idle processor, if a suitable + * one exists (and we can use cpus to check and, possibly, choose a new + * CPU, as we just &&-ed it with idlers). In fact, if we are on SMT, and + * cpu points to a busy thread with an idle sibling, both the threads + * will be considered the same, from the "idleness" calculation point + * of view", preventing vcpu from being moved to the thread that is + * actually idle. + * + * Notice that cpumask_test_cpu() is quicker than cpumask_empty(), so + * we check for it first. + */ + if ( !cpumask_test_cpu(cpu, &cpus) && !cpumask_empty(&cpus) ) + cpu = cpumask_cycle(cpu, &cpus); cpumask_clear_cpu(cpu, &cpus); while ( !cpumask_empty(&cpus) ) -- 2.30.2