xen: sched: leave CPUs doing tasklet work alone.

In both Credit1 and Credit2, stop considering a pCPU idle,
if the reason why the idle vCPU is being selected, is to
do tasklet work.

Not doing so means that the tickling and load balancing
logic, seeing the pCPU as idle, considers it a candidate
for picking up vCPUs. But the pCPU won't actually pick
up or schedule any vCPU, which would then remain in the
runqueue, which is bad, especially if there were other,
truly idle pCPUs, that could execute it.

The only drawback is that we can't assume that a pCPU is
in always marked as idle when being removed from an
instance of the Credit2 scheduler (csched2_deinit_pdata).
In fact, if we are in stop-machine (i.e., during suspend
or shutdown), the pCPUs are running the stopmachine_tasklet
and hence are actually marked as busy. On the other hand,
when removing a pCPU from a Credit2 pool, it will indeed
be idle. The only thing we can do, therefore, is to
remove the BUG_ON() check.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index ac227461776d77edd2f51d37be32c0d3e5241536..d547716e09f468ed17c467c30f44d78e8fe404e0 100644 (file)
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -1827,7 +1827,7 @@ csched_schedule(
      * Update idlers mask if necessary. When we're idling, other CPUs
      * will tickle us when they get extra work.
      */
-    if ( snext->pri == CSCHED_PRI_IDLE )
+    if ( !tasklet_work_scheduled && snext->pri == CSCHED_PRI_IDLE )
     {
         if ( !cpumask_test_cpu(cpu, prv->idlers) )
             cpumask_set_cpu(cpu, prv->idlers);

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 8b95a47f045b25655e953e48e63e5469171e9f04..7e572bf2abe4055b31f8c220b8b3a8fccce32a37 100644 (file)
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -1923,8 +1923,16 @@ csched2_schedule(
     }
     else
     {
-        /* Update the idle mask if necessary */
-        if ( !cpumask_test_cpu(cpu, &rqd->idle) )
+        /*
+         * Update the idle mask if necessary. Note that, if we're scheduling
+         * idle in order to carry on some tasklet work, we want to play busy!
+         */
+        if ( tasklet_work_scheduled )
+        {
+            if ( cpumask_test_cpu(cpu, &rqd->idle) )
+                cpumask_clear_cpu(cpu, &rqd->idle);
+        }
+        else if ( !cpumask_test_cpu(cpu, &rqd->idle) )
             cpumask_set_cpu(cpu, &rqd->idle);
         /* Make sure avgload gets updated periodically even
          * if there's no activity */
@@ -2304,8 +2312,6 @@ csched2_deinit_pdata(const struct scheduler *ops, void *pcpu, int cpu)
     /* No need to save IRQs here, they're already disabled */
     spin_lock(&rqd->lock);
 
-    BUG_ON(!cpumask_test_cpu(cpu, &rqd->idle));
-
     printk("Removing cpu %d from runqueue %d\n", cpu, rqi);
 
     cpumask_clear_cpu(cpu, &rqd->idle);