_csched_cpu_pick(): don't write idle bias more than once

For the bias to be really meaningful, it should be updated only when
the CPU selected will indeed be returned (and hence used for placing
the vCPU in question).

Signed-off-by: Jan Beulich <jbeulich@novell.com>

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index bfdd567e3e63f33035710cc12d7b65ba57752aa8..1d4d4236202e7419e8eae9a687ffd7aadac543bf 100644 (file)
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -464,6 +464,7 @@ _csched_cpu_pick(const struct scheduler *ops, struct vcpu *vc, bool_t commit)
     cpumask_t cpus;
     cpumask_t idlers;
     cpumask_t *online;
+    struct csched_pcpu *spc = NULL;
     int cpu;
 
     /*
@@ -531,9 +532,8 @@ _csched_cpu_pick(const struct scheduler *ops, struct vcpu *vc, bool_t commit)
                   && (weight_cpu * migrate_factor < weight_nxt) ) )
         {
             cpus_and(nxt_idlers, cpus, nxt_idlers);
-            cpu = cycle_cpu(CSCHED_PCPU(nxt)->idle_bias, nxt_idlers);
-            if ( commit )
-               CSCHED_PCPU(nxt)->idle_bias = cpu;
+            spc = CSCHED_PCPU(nxt);
+            cpu = cycle_cpu(spc->idle_bias, nxt_idlers);
             cpus_andnot(cpus, cpus, per_cpu(cpu_sibling_map, cpu));
         }
         else
@@ -542,6 +542,9 @@ _csched_cpu_pick(const struct scheduler *ops, struct vcpu *vc, bool_t commit)
         }
     }
 
+    if ( commit && spc )
+       spc->idle_bias = cpu;
+
     return cpu;
 }