[PATCH 2/2] RT: Add priority inheritance to the VFCIPI facility

[Gregory Haskins]

Signed-off-by: Gregory Haskins <[EMAIL PROTECTED]>
---

 kernel/vfcipi/thread.c |   52 +++++++++++++++++++++++++++++++++++++++++-------
 1 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/kernel/vfcipi/thread.c b/kernel/vfcipi/thread.c
index 0f1ef90..c8a3950 100644
--- a/kernel/vfcipi/thread.c
+++ b/kernel/vfcipi/thread.c
@@ -27,6 +27,7 @@
 #include <linux/irqflags.h>
 #include <linux/module.h>
 #include <linux/cpumask.h>
+#include <linux/syscalls.h>
 
 #include <asm/atomic.h>
 #include <asm/cmpxchg.h>
@@ -62,6 +63,7 @@ struct prio_array {
 struct vfcipi_task {
        raw_spinlock_t      lock;
        struct task_struct *task;
+       int                 prio;
        struct prio_array   rt_rq; /* Real-time request queue */
        struct list_head    rq;    /* Normal request queue */
 };
@@ -120,6 +122,7 @@ static void prio_array_enqueue(struct prio_array *array,
 {
        struct list_head *head;
 
+       BUG_ON(prio < 0);
        BUG_ON(prio > MAX_RT_PRIO);
 
        head = array->queue + prio;
@@ -220,9 +223,33 @@ static void vfcipi_workitem_wait(struct vfcipi_workitem 
*item, int wait)
                 * function completes entirely.
                 */
                vfcipi_status_wait(&item->finished);
+}
+
+/*
+ * ----------------------------------------
+ * priority-inheritance helpers
+ * ----------------------------------------
+ */
 
+/* Assumes ftask->lock is held */
+static void vfcipi_task_setprio(struct vfcipi_task *ftask, int prio)
+{
+       struct sched_param param = { 0, };
+       pid_t              pid   = ftask->task->pid;
+
+       if (ftask->prio != prio) {
+               if (prio != -1) {
+                       param.sched_priority = prio;
+                       sys_sched_setscheduler(pid, SCHED_FIFO, &param);
+               } else {
+                       sys_sched_setscheduler(pid, SCHED_NORMAL, &param);
+               }
+
+               ftask->prio = prio;
+       }
 }
 
+
 /*
  * ----------------------------------------
  * vfcipi_thread - daemon process for vfcipi per CPU
@@ -254,19 +281,29 @@ static int vfcipi_thread(void *data)
 
                if (!qi) {
                        /* Nothing to process for now.. */
+
+                       /* Set us back to normal priority */
+                       vfcipi_task_setprio(ftask, -1);
+
                        set_current_state(TASK_INTERRUPTIBLE);
                        spin_unlock(&ftask->lock);
                        schedule();
                        continue;
                }
 
+               item = qi->item;
+
+               /*
+                * Adjust the priority of our task based on what was pulled
+                * from the queue.  In theory, its our highest priority item
+                */
+               vfcipi_task_setprio(ftask, item->prio);
+
                spin_unlock(&ftask->lock);
 
                /*
-                * Extract the real pointer and discard the queueitem shell.
-                * We no longer need it.
+                * Discard the shell since the item is already extracted.
                 */
-               item = qi->item;
                vfcipi_heap_free(qi);
 
                /*
@@ -306,16 +343,14 @@ static int vfcipi_enqueue(struct vfcipi_workitem *item, 
int cpu)
 
        spin_lock(&ftask->lock);
 
-#ifdef NOT_YET
        if (rt_task(current)) {
-               item->prio = task_prio(current);
+               item->prio = current->rt_priority;
                prio_array_enqueue(&ftask->rt_rq, qi, item->prio);
 
                /* Priority inheritance on the kthread */
-               if (task_prio(ftask->task) < item->prio)
-                       set_prio_somehow(ftask->task, item->prio);
+               if (ftask->prio < item->prio)
+                       vfcipi_task_setprio(ftask, item->prio);
        } else
-#endif
                list_add_tail(&qi->list, &ftask->rq);
 
        wake_up_process(ftask->task);
@@ -427,6 +462,7 @@ int __init vfcipi_init(void)
                        goto out_free;
 
                spin_lock_init(&ftask->lock);
+               ftask->prio = -1;
                prio_array_init(&ftask->rt_rq);
                INIT_LIST_HEAD(&ftask->rq);
                per_cpu(vfcipi_tasks, cpu) = ftask;

-
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