On Fri, May 14, 2021 at 07:14:15PM -0700, Ricardo Neri wrote:
On Fri, May 14, 2021 at 11:47:45AM +0200, Peter Zijlstra wrote:
quoted
On Thu, May 13, 2021 at 08:49:08AM -0700, Ricardo Neri wrote:
quoted
include/linux/sched/topology.h | 1 +
kernel/sched/fair.c | 101 +++++++++++++++++++++++++++++++++
2 files changed, 102 insertions(+)
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 8f0f778b7c91..43bdb8b1e1df 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -57,6 +57,7 @@ static inline int cpu_numa_flags(void)
#endif
extern int arch_asym_cpu_priority(int cpu);
+extern bool arch_asym_check_smt_siblings(void);
struct sched_domain_attr {
int relax_domain_level;diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c8b66a5d593e..3d6cc027e6e6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -106,6 +106,15 @@ int __weak arch_asym_cpu_priority(int cpu)
return -cpu;
}
+/*
+ * For asym packing, first check the state of SMT siblings before deciding to
+ * pull tasks.
+ */
+bool __weak arch_asym_check_smt_siblings(void)
+{
+ return false;
+}
+
/*
* The margin used when comparing utilization with CPU capacity.
*
quoted
@@ -8458,6 +8550,9 @@ sched_asym(struct lb_env *env, struct sd_lb_stats *sds, struct sg_lb_stats *sgs
56 more quoted lines
As far as I can see, priorities in powerpc are set by the CPU number.
However, I am not sure how CPUs are enumerated? If CPUs in brackets are
SMT sibling, Does an enumeration looks like A) [0, 1], [2, 3] or B) [0, 2],
[1, 3]? I guess B is the right answer. Otherwise, both SMT siblings of a
core would need to be busy before a new core is used.
Still, I think the issue described in the cover letter may be
reproducible in powerpc as well. If CPU3 is offlined, and [0, 2] pulled
tasks from [1, -] so that both CPU0 and CPU2 become busy, CPU1 would not be
able to help since CPU0 has the highest priority.
I am cc'ing the linuxppc list to get some feedback.
Thanks and BR,
Ricardo