[Xen-changelog] [xen stable-4.8] xen: credit2: always mark a tickled pCPU as... tickled!

[patchbot@xxxxxxx]

commit 354c3e4c728b5e8f04dc8d9eabfa316e7823cbc5
Author:     Dario Faggioli <dario.faggioli@xxxxxxxxxx>
AuthorDate: Tue Mar 14 12:41:54 2017 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Mar 14 12:41:54 2017 +0100

    xen: credit2: always mark a tickled pCPU as... tickled!
    
    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>
    master commit: a76645240bd14e964e85dbc975a8989edea6aa27
    master date: 2017-03-01 16:56:34 +0000
---
 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 c669c38..25ea4d8 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -491,12 +491,15 @@ 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));
 }
 
 /*
@@ -900,6 +903,14 @@ __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:
@@ -1067,9 +1078,8 @@ 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);
@@ -1383,7 +1393,9 @@ 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));
@@ -1706,8 +1718,8 @@ 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
     {
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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