sched: Change rq->nr_running to unsigned int

tip:sched/core tip-bot for Peter Zijlstra 1 participant 1 message May 9, 2012 Scheduler

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2012-05-09 14:26 UTC #0 lore raw

Commit-ID:  c82513e513556a04f81aa511cd890acd23349c48
Gitweb:     http://git.kernel.org/tip/c82513e513556a04f81aa511cd890acd23349c48
Author:     Peter Zijlstra <[email protected]>
AuthorDate: Thu, 26 Apr 2012 13:12:27 +0200
Committer:  Ingo Molnar <[email protected]>
CommitDate: Wed, 9 May 2012 15:00:49 +0200

sched: Change rq->nr_running to unsigned int

Since there's a PID space limit of 30bits (see futex.h:FUTEX_TID_MASK) and allocating that many tasks (assuming a lower bound of 2 pages per task) would still take 8T of memory it seems reasonable to say that unsigned int is sufficient for rq->nr_running.

When we do get anywhere near that amount of tasks I suspect other things would go funny, load-balancer load computations would really need to be hoisted to 128bit etc.

So save a few bytes and convert rq->nr_running and friends to unsigned int.

Signed-off-by Peter Zijlstra <[email protected]>

Link http://lkml.kernel.org/n/[email protected] open here

Signed-off-by Ingo Molnar <[email protected]>

---
 kernel/sched/debug.c |    2 +-
 kernel/sched/fair.c  |    8 ++++----
 kernel/sched/sched.h |    6 +++---
 3 files changed, 8 insertions(+), 8 deletions(-)

kernel/sched/debug.c +1 -1

index 09acaa1..31e4f61 100644
@@ -202,7 +202,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 			SPLIT_NS(spread0));
 	SEQ_printf(m, "  .%-30s: %d\n", "nr_spread_over",
 			cfs_rq->nr_spread_over);
-	SEQ_printf(m, "  .%-30s: %ld\n", "nr_running", cfs_rq->nr_running);
+	SEQ_printf(m, "  .%-30s: %d\n", "nr_running", cfs_rq->nr_running);
 	SEQ_printf(m, "  .%-30s: %ld\n", "load", cfs_rq->load.weight);
 #ifdef CONFIG_FAIR_GROUP_SCHED
 #ifdef CONFIG_SMP

kernel/sched/fair.c +4 -4

index e955364..678966c 100644
@@ -4447,10 +4447,10 @@ redo:
 		 * correctly treated as an imbalance.
 		 */
 		env.flags |= LBF_ALL_PINNED;
-		env.load_move	= imbalance;
-		env.src_cpu	= busiest->cpu;
-		env.src_rq	= busiest;
-		env.loop_max	= min_t(unsigned long, sysctl_sched_nr_migrate, busiest->nr_running);
+		env.load_move = imbalance;
+		env.src_cpu   = busiest->cpu;
+		env.src_rq    = busiest;
+		env.loop_max  = min(sysctl_sched_nr_migrate, busiest->nr_running);
 
 more_balance:
 		local_irq_save(flags);

kernel/sched/sched.h +3 -3

index fb3acba..7282e7b 100644
@@ -201,7 +201,7 @@ struct cfs_bandwidth { };
 /* CFS-related fields in a runqueue */
 struct cfs_rq {
 	struct load_weight load;
-	unsigned long nr_running, h_nr_running;
+	unsigned int nr_running, h_nr_running;
 
 	u64 exec_clock;
 	u64 min_vruntime;

@@ -279,7 +279,7 @@ static inline int rt_bandwidth_enabled(void)
 /* Real-Time classes' related field in a runqueue: */
 struct rt_rq {
 	struct rt_prio_array active;
-	unsigned long rt_nr_running;
+	unsigned int rt_nr_running;
 #if defined CONFIG_SMP || defined CONFIG_RT_GROUP_SCHED
 	struct {
 		int curr; /* highest queued rt task prio */

@@ -353,7 +353,7 @@ struct rq {
 	 * nr_running and cpu_load should be in the same cacheline because
 	 * remote CPUs use both these fields when doing load calculation.
 	 */
-	unsigned long nr_running;
+	unsigned int nr_running;
 	#define CPU_LOAD_IDX_MAX 5
 	unsigned long cpu_load[CPU_LOAD_IDX_MAX];
 	unsigned long last_load_update_tick;