[Xen-changelog] [xen master] xen: sched: leave CPUs doing tasklet work alone.

[patchbot@xxxxxxx]

commit b047f888d4896d0e6cca10fbc996d4f1e1d769b2
Author:     Dario Faggioli <dario.faggioli@xxxxxxxxxx>
AuthorDate: Fri Jul 15 16:49:11 2016 +0200
Commit:     George Dunlap <george.dunlap@xxxxxxxxxx>
CommitDate: Mon Jul 18 17:50:10 2016 +0100

    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@xxxxxxxxxx>
    Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxx>
---
 xen/common/sched_credit.c  |  2 +-
 xen/common/sched_credit2.c | 14 ++++++++++----
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index ac22746..d547716 100644
--- 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 8b95a47..7e572bf 100644
--- 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);
--
generated by git-patchbot for /home/xen/git/xen.git#master

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