[Xen-devel] [PATCH 2/6] xen: credit2: make the cpu to runqueue map per-cpu

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

Instead of keeping an NR_CPUS big array of int-s,
directly inside csched2_private, use a per-cpu
variable.

That's especially beneficial (in terms of saved
memory) when there are more instance of Credit2 (in
different cpupools), and also helps fitting
csched2_private itself into CPU caches.

Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxx>
Cc: Anshul Makkar <anshulmakkar@xxxxxxxxx>
---
 xen/common/sched_credit2.c |   33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index 10d9488..15862f2 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -383,7 +383,6 @@ struct csched2_private {
     
     struct list_head sdom; /* Used mostly for dump keyhandler. */
 
-    int runq_map[NR_CPUS];
     cpumask_t active_queues; /* Queues which may have active cpus */
     struct csched2_runqueue_data *rqd;
 
@@ -393,6 +392,14 @@ struct csched2_private {
 };
 
 /*
+ * Physical CPU
+ *
+ * The only per-pCPU information we need to maintain is of which runqueue
+ * each CPU is part of.
+ */
+static DEFINE_PER_CPU(int, runq_map);
+
+/*
  * Virtual CPU
  */
 struct csched2_vcpu {
@@ -448,16 +455,16 @@ static inline struct csched2_dom *csched2_dom(const 
struct domain *d)
 }
 
 /* CPU to runq_id macro */
-static inline int c2r(const struct scheduler *ops, unsigned int cpu)
+static inline int c2r(unsigned int cpu)
 {
-    return csched2_priv(ops)->runq_map[(cpu)];
+    return per_cpu(runq_map, cpu);
 }
 
 /* CPU to runqueue struct macro */
 static inline struct csched2_runqueue_data *c2rqd(const struct scheduler *ops,
                                                   unsigned int cpu)
 {
-    return &csched2_priv(ops)->rqd[c2r(ops, cpu)];
+    return &csched2_priv(ops)->rqd[c2r(cpu)];
 }
 
 /*
@@ -1082,7 +1089,7 @@ runq_insert(const struct scheduler *ops, struct 
csched2_vcpu *svc)
     ASSERT(spin_is_locked(per_cpu(schedule_data, cpu).schedule_lock));
 
     ASSERT(!vcpu_on_runq(svc));
-    ASSERT(c2r(ops, cpu) == c2r(ops, svc->vcpu->processor));
+    ASSERT(c2r(cpu) == c2r(svc->vcpu->processor));
 
     ASSERT(&svc->rqd->runq == runq);
     ASSERT(!is_idle_vcpu(svc->vcpu));
@@ -1733,7 +1740,7 @@ csched2_cpu_pick(const struct scheduler *ops, struct vcpu 
*vc)
     if ( min_rqi == -1 )
     {
         new_cpu = get_fallback_cpu(svc);
-        min_rqi = c2r(ops, new_cpu);
+        min_rqi = c2r(new_cpu);
         min_avgload = prv->rqd[min_rqi].b_avgload;
         goto out_up;
     }
@@ -2622,7 +2629,7 @@ csched2_schedule(
             unsigned tasklet:8, idle:8, smt_idle:8, tickled:8;
         } d;
         d.cpu = cpu;
-        d.rq_id = c2r(ops, cpu);
+        d.rq_id = c2r(cpu);
         d.tasklet = tasklet_work_scheduled;
         d.idle = is_idle_vcpu(current);
         d.smt_idle = cpumask_test_cpu(cpu, &rqd->smt_idle);
@@ -2783,7 +2790,7 @@ dump_pcpu(const struct scheduler *ops, int cpu)
 #define cpustr keyhandler_scratch
 
     cpumask_scnprintf(cpustr, sizeof(cpustr), per_cpu(cpu_sibling_mask, cpu));
-    printk("CPU[%02d] runq=%d, sibling=%s, ", cpu, c2r(ops, cpu), cpustr);
+    printk("CPU[%02d] runq=%d, sibling=%s, ", cpu, c2r(cpu), cpustr);
     cpumask_scnprintf(cpustr, sizeof(cpustr), per_cpu(cpu_core_mask, cpu));
     printk("core=%s\n", cpustr);
 
@@ -2930,7 +2937,7 @@ init_pdata(struct csched2_private *prv, unsigned int cpu)
     }
     
     /* Set the runqueue map */
-    prv->runq_map[cpu] = rqi;
+    per_cpu(runq_map, cpu) = rqi;
     
     __cpumask_set_cpu(cpu, &rqd->idle);
     __cpumask_set_cpu(cpu, &rqd->active);
@@ -3034,7 +3041,7 @@ csched2_deinit_pdata(const struct scheduler *ops, void 
*pcpu, int cpu)
     ASSERT(!pcpu && cpumask_test_cpu(cpu, &prv->initialized));
     
     /* Find the old runqueue and remove this cpu from it */
-    rqi = prv->runq_map[cpu];
+    rqi = per_cpu(runq_map, cpu);
 
     rqd = prv->rqd + rqi;
 
@@ -3055,6 +3062,8 @@ csched2_deinit_pdata(const struct scheduler *ops, void 
*pcpu, int cpu)
     else if ( rqd->pick_bias == cpu )
         rqd->pick_bias = cpumask_first(&rqd->active);
 
+    per_cpu(runq_map, cpu) = -1;
+
     spin_unlock(&rqd->lock);
 
     __cpumask_clear_cpu(cpu, &prv->initialized);
@@ -3121,10 +3130,8 @@ csched2_init(struct scheduler *ops)
         return -ENOMEM;
     }
     for ( i = 0; i < nr_cpu_ids; i++ )
-    {
-        prv->runq_map[i] = -1;
         prv->rqd[i].id = -1;
-    }
+
     /* initialize ratelimit */
     prv->ratelimit_us = sched_ratelimit_us;
 


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