From 183b8ec38f1ec6c1f8419375303bf1d09a2b8369 Mon Sep 17 00:00:00 2001 From: Ricardo Neri Date: Fri, 10 Sep 2021 18:18:14 -0700 Subject: [PATCH] x86/sched: Decrease further the priorities of SMT siblings When scheduling, it is better to prefer a separate physical core rather than the SMT sibling of a high priority core. The existing formula to compute priorities takes such fact in consideration. There may exist, however, combinations of priorities (i.e., maximum frequencies) in which the priority of high-numbered SMT siblings of high-priority cores collides with the priority of low-numbered SMT siblings of low-priority cores. Consider for instance an SMT2 system with CPUs [0, 1] with priority 60 and [2, 3] with priority 30(CPUs in brackets are SMT siblings. In such a case, the resulting priorities would be [120, 60], [60, 30]. Thus, to ensure that CPU2 has higher priority than CPU1, divide the raw priority by the squared SMT iterator. The resulting priorities are [120, 30]. [60, 15]. Originally-by: Len Brown Signed-off-by: Len Brown Signed-off-by: Ricardo Neri Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210911011819.12184-2-ricardo.neri-calderon@linux.intel.com --- arch/x86/kernel/itmt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/itmt.c b/arch/x86/kernel/itmt.c index 1afbdd1dd777..9ff480e94511 100644 --- a/arch/x86/kernel/itmt.c +++ b/arch/x86/kernel/itmt.c @@ -198,7 +198,7 @@ void sched_set_itmt_core_prio(int prio, int core_cpu) * of the priority chain and only used when * all other high priority cpus are out of capacity. */ - smt_prio = prio * smp_num_siblings / i; + smt_prio = prio * smp_num_siblings / (i * i); per_cpu(sched_core_priority, cpu) = smt_prio; i++; }