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Subject[PATCH v2 6/7] x86/sched/itmt: Give all SMT siblings of a core the same priority
Date
Currently, each SMT sibling is given a priority that ensures that in
partially busy systems load is evenly spread among cores.

There is, however, no difference in performance among the SMT siblings of
a core.

Having different priorities for each SMT sibling triggers unnecessary
load balancing towards the higher-priority sibling.

Cc: Ben Segall <bsegall@google.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tim C. Chen <tim.c.chen@intel.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Len Brown <len.brown@intel.com>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
---
Changes since v1:
* Reworded commit message for clarity.
---
arch/x86/kernel/itmt.c | 23 +++++------------------
1 file changed, 5 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/itmt.c b/arch/x86/kernel/itmt.c
index 4cb5a5e4fa47..2be49ce4f94a 100644
--- a/arch/x86/kernel/itmt.c
+++ b/arch/x86/kernel/itmt.c
@@ -174,32 +174,19 @@ int arch_asym_cpu_priority(int cpu, bool check_smt)

/**
* sched_set_itmt_core_prio() - Set CPU priority based on ITMT
- * @prio: Priority of cpu core
- * @core_cpu: The cpu number associated with the core
+ * @prio: Priority of @cpu
+ * @cpu: The CPU number
*
* The pstate driver will find out the max boost frequency
* and call this function to set a priority proportional
- * to the max boost frequency. CPU with higher boost
+ * to the max boost frequency. CPUs with higher boost
* frequency will receive higher priority.
*
* No need to rebuild sched domain after updating
* the CPU priorities. The sched domains have no
* dependency on CPU priorities.
*/
-void sched_set_itmt_core_prio(int prio, int core_cpu)
+void sched_set_itmt_core_prio(int prio, int cpu)
{
- int cpu, i = 1;
-
- for_each_cpu(cpu, topology_sibling_cpumask(core_cpu)) {
- int smt_prio;
-
- /*
- * Ensure that the siblings are moved to the end
- * of the priority chain and only used when
- * all other high priority cpus are out of capacity.
- */
- smt_prio = prio * smp_num_siblings / (i * i);
- per_cpu(sched_core_priority, cpu) = smt_prio;
- i++;
- }
+ per_cpu(sched_core_priority, cpu) = prio;
}
--
2.25.1
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