sched: use a 2-d bitmap for searching lowest-pri CPU

The current code use a linear algorithm which causes scaling issues
on larger SMP machines.  This patch replaces that algorithm with a
2-dimensional bitmap to reduce latencies in the wake-up path.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Acked-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index aa960b84b881..8a1257b65560 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -74,6 +74,8 @@
 #include <asm/tlb.h>
 #include <asm/irq_regs.h>
 
+#include "sched_cpupri.h"
+
 /*
  * Convert user-nice values [ -20 ... 0 ... 19 ]
  * to static priority [ MAX_RT_PRIO..MAX_PRIO-1 ],
@@ -450,6 +452,9 @@ struct root_domain {
          */
         cpumask_t rto_mask;
         atomic_t rto_count;
+#ifdef CONFIG_SMP
+        struct cpupri cpupri;
+#endif
 };
 
 /*
@@ -6392,6 +6397,8 @@ static void init_rootdomain(struct root_domain *rd)
 
         cpus_clear(rd->span);
         cpus_clear(rd->online);
+
+        cpupri_init(&rd->cpupri);
 }
 
 static void init_defrootdomain(void)