[PATCH 08/16] xen: sched: prepare a .switch_sched hook for Credit2

[Dario Faggioli <dario.faggioli@citrix.com>]

RTDS is basically identical to Credit2, as far as scheduler
lock (re)mapping is concerned. Therefore, the same analisys
and considerations expressed for the previous patch ("xen:
sched: prepare a .switch_sched hook for Credit2"), applies
to it to.

This patch, therefore, introduces the switch_sched hook
for RTDS, as done already for Credit2 and Credit1.

Signed-off-by: Dario Faggioli <dario.faggioli@citrix.com>
---
Cc: George Dunlap <george.dunlap@eu.citrix.com>
Cc: Meng Xu <mengxu@cis.upenn.edu>
Cc: Tianyang Chen <tiche@seas.upenn.edu>
---
 xen/common/sched_rt.c |   31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/xen/common/sched_rt.c b/xen/common/sched_rt.c
index b6ac3ad..92be248 100644
--- a/xen/common/sched_rt.c
+++ b/xen/common/sched_rt.c
@@ -665,6 +665,36 @@ rt_init_pdata(const struct scheduler *ops, void *pdata, int cpu)
     spin_unlock_irqrestore(old_lock, flags);
 }
 
+/* Change the scheduler of cpu to us (RTDS). */
+static void
+rt_switch_sched(struct scheduler *new_ops, unsigned int cpu,
+                void *pdata, void *vdata)
+{
+    struct rt_vcpu *svc = vdata;
+    spinlock_t *old_lock;
+
+    ASSERT(!pdata && svc && is_idle_vcpu(svc->vcpu));
+
+    /*
+     * We may be acquiring the lock of another scheduler here (the one cpu
+     * still belongs to when calling this function). That is ok as, anyone
+     * trying to schedule on this cpu will block until when we release that
+     * lock (bottom of this function). When unblocked --because of the loop
+     * implemented by schedule_lock() functions-- he will notice the lock
+     * changed, and acquire ours before being able to proceed.
+     */
+    old_lock = pcpu_schedule_lock_irq(cpu);
+
+    idle_vcpu[cpu]->sched_priv = vdata;
+    per_cpu(scheduler, cpu) = new_ops;
+    per_cpu(schedule_data, cpu).sched_priv = NULL; /* no pdata */
+    /* (Re?)route the lock to our global lock. */
+    per_cpu(schedule_data, cpu).schedule_lock = &rt_priv(new_ops)->lock;
+
+    /* _Not_ pcpu_schedule_unlock(): schedule_lock may have changed! */
+    spin_unlock_irq(old_lock);
+}
+
 static void *
 rt_alloc_pdata(const struct scheduler *ops, int cpu)
 {
@@ -1400,6 +1430,7 @@ static const struct scheduler sched_rtds_def = {
     .alloc_pdata    = rt_alloc_pdata,
     .free_pdata     = rt_free_pdata,
     .init_pdata     = rt_init_pdata,
+    .switch_sched   = rt_switch_sched,
     .alloc_domdata  = rt_alloc_domdata,
     .free_domdata   = rt_free_domdata,
     .init_domain    = rt_dom_init,


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