[Xen-devel] [PATCH v4 1/7] xen: credit2: always mark a tickled pCPU as... tickled!

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

In fact, whether or not a pCPU has been tickled, and is
therefore about to re-schedule, is something we look at
and base decisions on in various places.

So, let's make sure that we do that basing on accurate
information.

While there, also tweak a little bit smt_idle_mask_clear()
(used for implementing SMT support), so that it only alter
the relevant cpumask when there is the actual need for this.
(This is only for reduced overhead, behavior remains the
same).

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
Reviewed-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
Cc: Anshul Makkar <anshul.makkar@xxxxxxxxxx>
---
Changes from v3:
* moved at the top of the series.

Changes from v2:
* fixed a bug I found myself in runq_tickle().
---
 xen/common/sched_credit2.c |   26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index b12d038..cfb783d 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -504,12 +504,15 @@ void smt_idle_mask_set(unsigned int cpu, const cpumask_t 
*idlers,
 }
 
 /*
- * Clear the bits of all the siblings of cpu from mask.
+ * Clear the bits of all the siblings of cpu from mask (if necessary).
  */
 static inline
 void smt_idle_mask_clear(unsigned int cpu, cpumask_t *mask)
 {
-    cpumask_andnot(mask, mask, per_cpu(cpu_sibling_mask, cpu));
+    const cpumask_t *cpu_siblings = per_cpu(cpu_sibling_mask, cpu);
+
+    if ( cpumask_subset(cpu_siblings, mask) )
+        cpumask_andnot(mask, mask, per_cpu(cpu_sibling_mask, cpu));
 }
 
 /*
@@ -913,6 +916,14 @@ __runq_remove(struct csched2_vcpu *svc)
 
 void burn_credits(struct csched2_runqueue_data *rqd, struct csched2_vcpu *, 
s_time_t);
 
+static inline void
+tickle_cpu(unsigned int cpu, struct csched2_runqueue_data *rqd)
+{
+    __cpumask_set_cpu(cpu, &rqd->tickled);
+    smt_idle_mask_clear(cpu, &rqd->smt_idle);
+    cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ);
+}
+
 /*
  * Check what processor it is best to 'wake', for picking up a vcpu that has
  * just been put (back) in the runqueue. Logic is as follows:
@@ -1080,9 +1091,8 @@ runq_tickle(const struct scheduler *ops, struct 
csched2_vcpu *new, s_time_t now)
                     sizeof(d),
                     (unsigned char *)&d);
     }
-    __cpumask_set_cpu(ipid, &rqd->tickled);
-    smt_idle_mask_clear(ipid, &rqd->smt_idle);
-    cpu_raise_softirq(ipid, SCHEDULE_SOFTIRQ);
+
+    tickle_cpu(ipid, rqd);
 
     if ( unlikely(new->tickled_cpu != -1) )
         SCHED_STAT_CRANK(tickled_cpu_overwritten);
@@ -1395,7 +1405,9 @@ csched2_vcpu_sleep(const struct scheduler *ops, struct 
vcpu *vc)
     SCHED_STAT_CRANK(vcpu_sleep);
 
     if ( curr_on_cpu(vc->processor) == vc )
-        cpu_raise_softirq(vc->processor, SCHEDULE_SOFTIRQ);
+    {
+        tickle_cpu(vc->processor, svc->rqd);
+    }
     else if ( __vcpu_on_runq(svc) )
     {
         ASSERT(svc->rqd == RQD(ops, vc->processor));
@@ -1718,8 +1730,8 @@ static void migrate(const struct scheduler *ops,
         svc->migrate_rqd = trqd;
         __set_bit(_VPF_migrating, &svc->vcpu->pause_flags);
         __set_bit(__CSFLAG_runq_migrate_request, &svc->flags);
-        cpu_raise_softirq(cpu, SCHEDULE_SOFTIRQ);
         SCHED_STAT_CRANK(migrate_requested);
+        tickle_cpu(cpu, svc->rqd);
     }
     else
     {


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