[xen master] xen/sched: try harder to find a runnable unit in rt_schedule()

[patchbot@xxxxxxx]

commit 0f1dec89d324d93fa056334ac384c6845f480fe8
Author:     Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Fri Dec 2 10:29:19 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Dec 2 10:29:19 2022 +0100

    xen/sched: try harder to find a runnable unit in rt_schedule()
    
    Instead of directly falling back to the idle unit in case the top
    unit from the run queue happened to be not runnable, consult the run
    queue again.
    
    Suggested-by: Dario Faggioli <dfaggioli@xxxxxxxx>
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>
---
 xen/common/sched/rt.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/xen/common/sched/rt.c b/xen/common/sched/rt.c
index 05988cbd3d..d443cd5831 100644
--- a/xen/common/sched/rt.c
+++ b/xen/common/sched/rt.c
@@ -1101,15 +1101,20 @@ rt_schedule(const struct scheduler *ops, struct 
sched_unit *currunit,
     }
     else
     {
-        snext = runq_pick(ops, cpumask_of(sched_cpu), cur_cpu);
-
-        if ( snext == NULL )
-            snext = rt_unit(sched_idle_unit(sched_cpu));
-        else if ( !unit_runnable_state(snext->unit) )
+        while ( true )
         {
+            snext = runq_pick(ops, cpumask_of(sched_cpu), cur_cpu);
+
+            if ( snext == NULL )
+            {
+                snext = rt_unit(sched_idle_unit(sched_cpu));
+                break;
+            }
+            if ( unit_runnable_state(snext->unit) )
+                break;
+
             q_remove(snext);
             replq_remove(ops, snext);
-            snext = rt_unit(sched_idle_unit(sched_cpu));
         }
 
         /* if scurr has higher priority and budget, still pick scurr */
--
generated by git-patchbot for /home/xen/git/xen.git#master