The following commit has been merged into the sched/core branch of tip: Commit-ID: 014bfe892220077b8c623b97e31a91378d204137 Gitweb: https://git.kernel.org/tip/014bfe892220077b8c623b97e31a91378d204137 Author: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx> AuthorDate: Fri, 10 Sep 2021 18:18:14 -07:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Sat, 18 Sep 2021 12:18:39 +02:00 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 <len.brown@xxxxxxxxx> Signed-off-by: Len Brown <len.brown@xxxxxxxxx> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20210911011819.12184-2-ricardo.neri-calderon@xxxxxxxxxxxxxxx --- 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 1afbdd1..9ff480e 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++; }