[Xen-devel] [PATCH 02/24] xen: credit1: fix mask to be used for tickling in Credit1

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

If there are idle pcpus inside the waking vcpu's
soft-affinity mask, we should really tickle one
of them (this is one of the purposes of the
__runq_tickle() function itself!), not just
any idle pcpu.

The issue has been introduced in 02ea5031825d
("credit1: properly deal with pCPUs not in any cpupool"),
where the usage of idle_mask is changed, without
updating the bottom of the function, where it
is also referenced.

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
---
David, a while ago you asked what could have been that was causing awful
results for Credit1, for CPU bound workloads, in the overloaded scenario of one
of my benchmarks. I think the bug fixed either here or in next patch (but I'd
be rather sure it's this one) is where the problem was. :-)
---
 xen/common/sched_credit.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c
index 6eccf09..3d4f223 100644
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -454,11 +454,12 @@ static inline void __runq_tickle(struct csched_vcpu *new)
                 if ( opt_tickle_one_idle )
                 {
                     this_cpu(last_tickle_cpu) =
-                        cpumask_cycle(this_cpu(last_tickle_cpu), &idle_mask);
+                        cpumask_cycle(this_cpu(last_tickle_cpu),
+                                      cpumask_scratch_cpu(cpu));
                     __cpumask_set_cpu(this_cpu(last_tickle_cpu), &mask);
                 }
                 else
-                    cpumask_or(&mask, &mask, &idle_mask);
+                    cpumask_or(&mask, &mask, cpumask_scratch_cpu(cpu));
             }
 
             /* Did we find anyone? */


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