[Xen-changelog] [xen-unstable] _csched_cpu_pick(): don't write idle bias more than once

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxxxx>
# Date 1300123187 0
# Node ID 77bb4be5c95430ee3bad473f1c791affaa517034
# Parent  c40da47621d8cb06445e32aa87eba049b1aa5370
_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@xxxxxxxxxx>
---


diff -r c40da47621d8 -r 77bb4be5c954 xen/common/sched_credit.c
--- a/xen/common/sched_credit.c Mon Mar 14 17:19:22 2011 +0000
+++ b/xen/common/sched_credit.c Mon Mar 14 17:19:47 2011 +0000
@@ -464,6 +464,7 @@
     cpumask_t cpus;
     cpumask_t idlers;
     cpumask_t *online;
+    struct csched_pcpu *spc = NULL;
     int cpu;
 
     /*
@@ -531,9 +532,8 @@
                   && (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 @@
         }
     }
 
+    if ( commit && spc )
+       spc->idle_bias = cpu;
+
     return cpu;
 }
 

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