xen: add real time scheduler rtds

This scheduler follows the Preemptive Global Earliest Deadline First
(EDF) theory in real-time field.
At any scheduling point, the VCPU with earlier deadline has higher
priority. The scheduler always picks the highest priority VCPU to run on a
feasible PCPU.
A PCPU is feasible if the VCPU can run on this PCPU and (the PCPU is
idle or has a lower-priority VCPU running on it.)

Each VCPU has a dedicated period and budget.
The deadline of a VCPU is at the end of each period;
A VCPU has its budget replenished at the beginning of each period;
While scheduled, a VCPU burns its budget.
The VCPU needs to finish its budget before its deadline in each period;
The VCPU discards its unused budget at the end of each period.
If a VCPU runs out of budget in a period, it has to wait until next period.

Each VCPU is implemented as a deferable server.
When a VCPU has a task running on it, its budget is continuously burned;
When a VCPU has no task but with budget left, its budget is preserved.

Queue scheme:
A global runqueue and a global depletedq for each CPU pool.
The runqueue holds all runnable VCPUs with budget and sorted by deadline;
The depletedq holds all VCPUs without budget and unsorted.

Note: cpumask and cpupool is supported.

This is an experimental scheduler.

Signed-off-by: Meng Xu <mengxu@cis.upenn.edu>
Signed-off-by: Sisu Xi <xisisu@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Tested-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>
[ ijc -- use PRI_stime to print delta in burn_budget, to fix build on
         32-bit (i.e. arm32) ]

xen/common/Makefile

@@ -26,6 +26,7 @@ obj-y += sched_credit.o
 obj-y += sched_credit2.o
 obj-y += sched_sedf.o
 obj-y += sched_arinc653.o
+obj-y += sched_rt.o
 obj-y += schedule.o
 obj-y += shutdown.o
 obj-y += softirq.o

xen/common/schedule.c

@@ -69,6 +69,7 @@ static const struct scheduler *schedulers[] = {
     &sched_credit_def,
     &sched_credit2_def,
     &sched_arinc653_def,
+    &sched_rtds_def,
 };
 
 static struct scheduler __read_mostly ops;

xen/include/public/domctl.h

@@ -347,6 +347,8 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_max_vcpus_t);
 #define XEN_SCHEDULER_CREDIT   5
 #define XEN_SCHEDULER_CREDIT2  6
 #define XEN_SCHEDULER_ARINC653 7
+#define XEN_SCHEDULER_RTDS     8
+
 /* Set or get info? */
 #define XEN_DOMCTL_SCHEDOP_putinfo 0
 #define XEN_DOMCTL_SCHEDOP_getinfo 1
@@ -368,6 +370,10 @@ struct xen_domctl_scheduler_op {
         struct xen_domctl_sched_credit2 {
             uint16_t weight;
         } credit2;
+        struct xen_domctl_sched_rtds {
+            uint32_t period;
+            uint32_t budget;
+        } rtds;
     } u;
 };
 typedef struct xen_domctl_scheduler_op xen_domctl_scheduler_op_t;

xen/include/public/trace.h

@@ -77,6 +77,7 @@
 #define TRC_SCHED_CSCHED2  1
 #define TRC_SCHED_SEDF     2
 #define TRC_SCHED_ARINC653 3
+#define TRC_SCHED_RTDS     4
 
 /* Per-scheduler tracing */
 #define TRC_SCHED_CLASS_EVT(_c, _e) \

xen/include/xen/sched-if.h

@@ -169,6 +169,7 @@ extern const struct scheduler sched_sedf_def;
 extern const struct scheduler sched_credit_def;
 extern const struct scheduler sched_credit2_def;
 extern const struct scheduler sched_arinc653_def;
+extern const struct scheduler sched_rtds_def;
 
 
 struct cpupool