Xen devel - Mar 2011 - [PATCH 2/3] _csched_cpu_pick(): don''t write idle bias more than once

For the bias to be really meaningful, it should be updated onbly 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>

--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -464,6 +464,7 @@ _csched_cpu_pick(const struct scheduler 
     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 
                   && (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 
         }
     }
 
+    if ( commit && spc )
+       spc->idle_bias = cpu;
+
     return cpu;
 }
 





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