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].
Cc: Aubrey Li <aubrey...@intel.com>
Cc: Ben Segall <bseg...@google.com>
Cc: Daniel Bristot de Oliveira <bris...@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggem...@arm.com>
Cc: Joel Fernandes (Google) <j...@joelfernandes.org>
Cc: Mel Gorman <mgor...@suse.de>
Cc: Quentin Perret <qper...@google.com>
Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
Cc: Srinivas Pandruvada <srinivas.pandruv...@linux.intel.com>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Tim Chen <tim.c.c...@linux.intel.com>
Originally-by: Len Brown <len.br...@intel.com>
Signed-off-by: Len Brown <len.br...@intel.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calde...@linux.intel.com>
---
Changes since v4:
* None
Changes since v3:
* Introduced this patch
Changes since v2:
* N/A
Changes since v1:
* N/A
---
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++;
}
--
2.17.1
