sched/fair, cpumask: Export for_each_cpu_wrap()

More users for for_each_cpu_wrap() have appeared. Promote the construct
to generic cpumask interface.

The implementation is slightly modified to reduce arguments.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Lauro Ramos Venancio <lvenanci@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: lwang@redhat.com
Link: http://lkml.kernel.org/r/20170414122005.o35me2h5nowqkxbv@hirez.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 2404ad238c0b8c0309e8c1480339a19967968edf..a21b1fb9a9689fdf1bf8157c8b5457bd053784e2 100644 (file)
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -236,6 +236,23 @@ unsigned int cpumask_local_spread(unsigned int i, int node);
                (cpu) = cpumask_next_zero((cpu), (mask)),       \
                (cpu) < nr_cpu_ids;)
 
+extern int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap);
+
+/**
+ * for_each_cpu_wrap - iterate over every cpu in a mask, starting at a specified location
+ * @cpu: the (optionally unsigned) integer iterator
+ * @mask: the cpumask poiter
+ * @start: the start location
+ *
+ * The implementation does not assume any bit in @mask is set (including @start).
+ *
+ * After the loop, cpu is >= nr_cpu_ids.
+ */
+#define for_each_cpu_wrap(cpu, mask, start)                                    \
+       for ((cpu) = cpumask_next_wrap((start)-1, (mask), (start), false);      \
+            (cpu) < nr_cpumask_bits;                                           \
+            (cpu) = cpumask_next_wrap((cpu), (mask), (start), true))
+
 /**
  * for_each_cpu_and - iterate over every cpu in both masks
  * @cpu: the (optionally unsigned) integer iterator

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4f1825d6093799d09f9de0239bca127ec3ad10fc..f80c825e2b43b73230ccb26e1f814098b3a194dd 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5640,43 +5640,6 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
        return shallowest_idle_cpu != -1 ? shallowest_idle_cpu : least_loaded_cpu;
 }
 
-/*
- * Implement a for_each_cpu() variant that starts the scan at a given cpu
- * (@start), and wraps around.
- *
- * This is used to scan for idle CPUs; such that not all CPUs looking for an
- * idle CPU find the same CPU. The down-side is that tasks tend to cycle
- * through the LLC domain.
- *
- * Especially tbench is found sensitive to this.
- */
-
-static int cpumask_next_wrap(int n, const struct cpumask *mask, int start, int *wrapped)
-{
-       int next;
-
-again:
-       next = find_next_bit(cpumask_bits(mask), nr_cpumask_bits, n+1);
-
-       if (*wrapped) {
-               if (next >= start)
-                       return nr_cpumask_bits;
-       } else {
-               if (next >= nr_cpumask_bits) {
-                       *wrapped = 1;
-                       n = -1;
-                       goto again;
-               }
-       }
-
-       return next;
-}
-
-#define for_each_cpu_wrap(cpu, mask, start, wrap)                              \
-       for ((wrap) = 0, (cpu) = (start)-1;                                     \
-               (cpu) = cpumask_next_wrap((cpu), (mask), (start), &(wrap)),     \
-               (cpu) < nr_cpumask_bits; )
-
 #ifdef CONFIG_SCHED_SMT
 
 static inline void set_idle_cores(int cpu, int val)
@@ -5736,7 +5699,7 @@ unlock:
 static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int target)
 {
        struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
-       int core, cpu, wrap;
+       int core, cpu;
 
        if (!static_branch_likely(&sched_smt_present))
                return -1;
@@ -5746,7 +5709,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
 
        cpumask_and(cpus, sched_domain_span(sd), &p->cpus_allowed);
 
-       for_each_cpu_wrap(core, cpus, target, wrap) {
+       for_each_cpu_wrap(core, cpus, target) {
                bool idle = true;
 
                for_each_cpu(cpu, cpu_smt_mask(core)) {
@@ -5812,7 +5775,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
        u64 avg_cost, avg_idle = this_rq()->avg_idle;
        u64 time, cost;
        s64 delta;
-       int cpu, wrap;
+       int cpu;
 
        this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
        if (!this_sd)
@@ -5829,7 +5792,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 
        time = local_clock();
 
-       for_each_cpu_wrap(cpu, sched_domain_span(sd), target, wrap) {
+       for_each_cpu_wrap(cpu, sched_domain_span(sd), target) {
                if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
                        continue;
                if (idle_cpu(cpu))

diff --git a/lib/cpumask.c b/lib/cpumask.c
index 81dedaab36ccfed3150281a0f915a4070f667bfd..4731a0895760e70cab07d59a0cff45c2590da450 100644 (file)
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -43,6 +43,38 @@ int cpumask_any_but(const struct cpumask *mask, unsigned int cpu)
 }
 EXPORT_SYMBOL(cpumask_any_but);
 
+/**
+ * cpumask_next_wrap - helper to implement for_each_cpu_wrap
+ * @n: the cpu prior to the place to search
+ * @mask: the cpumask pointer
+ * @start: the start point of the iteration
+ * @wrap: assume @n crossing @start terminates the iteration
+ *
+ * Returns >= nr_cpu_ids on completion
+ *
+ * Note: the @wrap argument is required for the start condition when
+ * we cannot assume @start is set in @mask.
+ */
+int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool wrap)
+{
+       int next;
+
+again:
+       next = cpumask_next(n, mask);
+
+       if (wrap && n < start && next >= start) {
+               return nr_cpumask_bits;
+
+       } else if (next >= nr_cpumask_bits) {
+               wrap = true;
+               n = -1;
+               goto again;
+       }
+
+       return next;
+}
+EXPORT_SYMBOL(cpumask_next_wrap);
+
 /* These are not inline because of header tangles. */
 #ifdef CONFIG_CPUMASK_OFFSTACK
 /**