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[Xen-devel] [PATCH v3 06/11] xen: sched: on Credit2, don't reprogram the timer if idle

as other schedulers are doing already: if the idle vcpu
is picked and scheduled, there is no need to reprogram the
scheduler timer to fire and invoke csched2_schedule()
again in future.

Tickling or external events will serve as pokes, when
necessary, but until we can, we should just stay idle.

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Reported-by: Tianyang Chen <tiche@xxxxxxxxxxxxxx>
Suggested-by: George Dunlap <george.dunlap@xxxxxxxxxx>
Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>
Cc: Tianyang Chen <tiche@xxxxxxxxxxxxxx>
Changes from v1:
 * use George's work address (sorry again!).
 xen/common/sched_credit2.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 7286e50..b207d84 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -1543,8 +1543,12 @@ csched2_runtime(const struct scheduler *ops, int cpu, 
struct csched2_vcpu *snext
     struct csched2_runqueue_data *rqd = RQD(ops, cpu);
     struct list_head *runq = &rqd->runq;
+    /*
+     * If we're idle, just stay so. Others (or external events)
+     * will poke us when necessary.
+     */
     if ( is_idle_vcpu(snext->vcpu) )
-        return CSCHED2_MAX_TIMER;
+        return -1;
     /* General algorithm:
      * 1) Run until snext's credit will be 0

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