[Xen-devel] [PATCH 19/19] xen: credit2: use cpumask_first instead of cpumask_any when choosing cpu

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

because it is cheaper, and there is no much point in
randomizing which cpu gets selected anyway, as such
choice will be overridden shortly after, in runq_tickle().

If we really feel the need (e.g., we prove it worth with
benchmarking), we can record the last cpu which was used
by csched2_cpu_pick() and migrate() in a per-runq variable,
and then use cpumask_cycle()... but this really does not
look necessary.

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
Cc: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 xen/common/sched_credit2.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index a8b3a85..afd432e 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -1545,7 +1545,7 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu 
*vc)
         {
             cpumask_and(cpumask_scratch, vc->cpu_hard_affinity,
                         &svc->migrate_rqd->active);
-            new_cpu = cpumask_any(cpumask_scratch);
+            new_cpu = cpumask_first(cpumask_scratch);
             if ( new_cpu < nr_cpu_ids )
                 goto out_up;
         }
@@ -1604,7 +1604,7 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu 
*vc)
 
     cpumask_and(cpumask_scratch, vc->cpu_hard_affinity,
                 &prv->rqd[min_rqi].active);
-    new_cpu = cpumask_any(cpumask_scratch);
+    new_cpu = cpumask_first(cpumask_scratch);
     BUG_ON(new_cpu >= nr_cpu_ids);
 
  out_up:
@@ -1718,7 +1718,7 @@ static void migrate(const struct scheduler *ops,
 
         cpumask_and(cpumask_scratch, svc->vcpu->cpu_hard_affinity,
                     &trqd->active);
-        svc->vcpu->processor = cpumask_any(cpumask_scratch);
+        svc->vcpu->processor = cpumask_first(cpumask_scratch);
         ASSERT(svc->vcpu->processor < nr_cpu_ids);
 
         __runq_assign(svc, trqd);


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