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diff --git a/sys/kern/kern_cpuset.c b/sys/kern/kern_cpuset.c
--- a/sys/kern/kern_cpuset.c
+++ b/sys/kern/kern_cpuset.c
@@ -310,6 +310,19 @@
return (set);
}
+/*
+ * Keep CPU_SET_ONECPU in step with cs_mask. Called wherever the mask changes.
+ */
+static void
+cpuset_flags_update(struct cpuset *set)
+{
+
+ if (CPU_COUNT(&set->cs_mask) == 1)
+ set->cs_flags |= CPU_SET_ONECPU;
+ else
+ set->cs_flags &= ~CPU_SET_ONECPU;
+}
+
/*
* Initialize a set in the space provided in 'set' with the provided parameters.
* The set is returned with a single ref. May return EDEADLK if the set
@@ -336,6 +349,7 @@
mtx_lock_spin(&cpuset_lock);
set->cs_domain = domain;
CPU_AND(&set->cs_mask, &set->cs_mask, &parent->cs_mask);
+ cpuset_flags_update(set);
set->cs_id = id;
set->cs_parent = cpuset_ref(parent);
LIST_INSERT_HEAD(&parent->cs_children, set, cs_siblings);
@@ -677,6 +691,7 @@
mtx_assert(&cpuset_lock, MA_OWNED);
CPU_AND(&set->cs_mask, &set->cs_mask, mask);
+ cpuset_flags_update(set);
LIST_FOREACH(nset, &set->cs_children, cs_siblings)
cpuset_update(nset, &set->cs_mask);
@@ -1659,6 +1674,7 @@
LIST_INSERT_HEAD(&cpuset_ids, set, cs_link);
refcount_init(&set->cs_ref, 1);
set->cs_flags = CPU_SET_ROOT | CPU_SET_RDONLY;
+ cpuset_flags_update(set);
set->cs_domain = domainset0;
cpuset_zero = set;
cpuset_root = &set->cs_mask;
diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -1404,6 +1404,7 @@
SCHED_STAT_DEFINE(pickcpu_lowest, "Selected lowest load");
SCHED_STAT_DEFINE(pickcpu_local, "Migrated to current cpu");
SCHED_STAT_DEFINE(pickcpu_migration, "Selection may have caused migration");
+SCHED_STAT_DEFINE(pickcpu_onecpu, "Cpuset allows a single cpu");
static int
sched_pickcpu(struct thread *td, int flags)
@@ -1425,6 +1426,15 @@
*/
if ((flags & SRQ_OURSELF) || !THREAD_CAN_MIGRATE(td))
return (ts->ts_cpu);
+ /*
+ * A thread whose cpuset holds one cpu can only run there, so skip
+ * the topology search.
+ */
+ mask = &td->td_cpuset->cs_mask;
+ if (td->td_cpuset->cs_flags & CPU_SET_ONECPU) {
+ SCHED_STAT_INC(pickcpu_onecpu);
+ return (CPU_FFS(mask) - 1);
+ }
/*
* Prefer to run interrupt threads on the processors that generate
* the interrupt.
@@ -1490,7 +1500,6 @@
if (ccg == cpu_top)
ccg = NULL;
cpu = -1;
- mask = &td->td_cpuset->cs_mask;
pri = td->td_priority;
r = TD_IS_RUNNING(td);
/*
diff --git a/sys/sys/cpuset.h b/sys/sys/cpuset.h
--- a/sys/sys/cpuset.h
+++ b/sys/sys/cpuset.h
@@ -149,6 +149,7 @@
#define CPU_SET_ROOT 0x0001 /* Set is a root set. */
#define CPU_SET_RDONLY 0x0002 /* No modification allowed. */
+#define CPU_SET_ONECPU 0x0004 /* Mask holds a single cpu. */
extern cpuset_t *cpuset_root;
struct prison;

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