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Subject[PATCH] 2.4-ac task->cpu abstraction and optimization
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Alan,

Implement "task_cpu()" and "set_task_cpu()" as wrappers for reading and
writing task->cpu, respectively.

Additionally, introduce a nice optimization: on UP, task_cpu() can
hard-code to "0" and set_task_cpu() can be a no-op.

Patch is against 2.4.20-pre5-ac4, please apply.

Robert Love

diff -urN linux-2.4.20-pre5-ac4-rml/Documentation/sched-coding.txt linux/Documentation/sched-coding.txt
--- linux-2.4.20-pre5-ac4-rml/Documentation/sched-coding.txt Wed Sep 11 17:39:05 2002
+++ linux/Documentation/sched-coding.txt Wed Sep 11 17:39:25 2002
@@ -88,12 +88,13 @@
Returns the runqueue of the specified cpu.
this_rq()
Returns the runqueue of the current cpu.
-task_rq(pid)
- Returns the runqueue which holds the specified pid.
+task_rq(task)
+ Returns the runqueue which holds the specified task.
cpu_curr(cpu)
Returns the task currently running on the given cpu.
-rt_task(pid)
- Returns true if pid is real-time, false if not.
+rt_task(task)
+ Returns true if task is real-time, false if not.
+task_cpu(task)


Process Control Methods
@@ -117,6 +118,8 @@
Clears need_resched in the given task.
void set_need_resched()
Sets need_resched in the current task.
+void set_task_cpu(task, cpu)
+ Sets task->cpu to cpu on SMP. Noop on UP.
void clear_need_resched()
Clears need_resched in the current task.
int need_resched()
diff -urN linux-2.4.20-pre5-ac4-rml/fs/proc/array.c linux/fs/proc/array.c
--- linux-2.4.20-pre5-ac4-rml/fs/proc/array.c Wed Sep 11 17:38:21 2002
+++ linux/fs/proc/array.c Wed Sep 11 17:39:25 2002
@@ -389,7 +389,7 @@
task->nswap,
task->cnswap,
task->exit_signal,
- task->cpu);
+ task_cpu(task));
if(mm)
mmput(mm);
return res;
diff -urN linux-2.4.20-pre5-ac4-rml/include/linux/sched.h linux/include/linux/sched.h
--- linux-2.4.20-pre5-ac4-rml/include/linux/sched.h Wed Sep 11 17:40:52 2002
+++ linux/include/linux/sched.h Wed Sep 11 17:39:25 2002
@@ -976,6 +976,34 @@
return unlikely(current->need_resched);
}

+/*
+ * Wrappers for p->cpu access. No-op on UP.
+ */
+#ifdef CONFIG_SMP
+
+static inline unsigned int task_cpu(struct task_struct *p)
+{
+ return p->cpu;
+}
+
+static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
+{
+ p->cpu = cpu;
+}
+
+#else
+
+static inline unsigned int task_cpu(struct task_struct *p)
+{
+ return 0;
+}
+
+static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
+{
+}
+
+#endif /* CONFIG_SMP */
+
#endif /* __KERNEL__ */

#endif
diff -urN linux-2.4.20-pre5-ac4-rml/kernel/sched.c linux/kernel/sched.c
--- linux-2.4.20-pre5-ac4-rml/kernel/sched.c Wed Sep 11 17:40:57 2002
+++ linux/kernel/sched.c Wed Sep 11 17:40:33 2002
@@ -148,7 +148,7 @@

#define cpu_rq(cpu) (runqueues + (cpu))
#define this_rq() cpu_rq(smp_processor_id())
-#define task_rq(p) cpu_rq((p)->cpu)
+#define task_rq(p) cpu_rq(task_cpu(p))
#define cpu_curr(cpu) (cpu_rq(cpu)->curr)
#define rt_task(p) ((p)->prio < MAX_RT_PRIO)

@@ -311,8 +311,8 @@
need_resched = p->need_resched;
wmb();
set_tsk_need_resched(p);
- if (!need_resched && (p->cpu != smp_processor_id()))
- smp_send_reschedule(p->cpu);
+ if (!need_resched && (task_cpu(p) != smp_processor_id()))
+ smp_send_reschedule(task_cpu(p));
#else
set_tsk_need_resched(p);
#endif
@@ -391,10 +391,10 @@
* currently. Do not violate hard affinity.
*/
if (unlikely(sync && (rq->curr != p) &&
- (p->cpu != smp_processor_id()) &&
+ (task_cpu(p) != smp_processor_id()) &&
(p->cpus_allowed & (1UL << smp_processor_id())))) {

- p->cpu = smp_processor_id();
+ set_task_cpu(p, smp_processor_id());
task_rq_unlock(rq, &flags);
goto repeat_lock_task;
}
@@ -437,7 +437,7 @@
p->sleep_avg = p->sleep_avg * CHILD_PENALTY / 100;
p->prio = effective_prio(p);
}
- p->cpu = smp_processor_id();
+ set_task_cpu(p, smp_processor_id());
activate_task(p, rq);

rq_unlock(rq);
@@ -727,7 +727,7 @@
*/
dequeue_task(next, array);
busiest->nr_running--;
- next->cpu = this_cpu;
+ set_task_cpu(next, this_cpu);
this_rq->nr_running++;
enqueue_task(next, this_rq->active);
if (next->prio < current->prio)
@@ -1718,7 +1718,7 @@

void __init init_idle(task_t *idle, int cpu)
{
- runqueue_t *idle_rq = cpu_rq(cpu), *rq = cpu_rq(idle->cpu);
+ runqueue_t *idle_rq = cpu_rq(cpu), *rq = cpu_rq(task_cpu(idle));
unsigned long flags;

__save_flags(flags);
@@ -1730,7 +1730,7 @@
idle->array = NULL;
idle->prio = MAX_PRIO;
idle->state = TASK_RUNNING;
- idle->cpu = cpu;
+ set_task_cpu(idle, cpu);
double_rq_unlock(idle_rq, rq);
set_tsk_need_resched(idle);
__restore_flags(flags);
@@ -1835,7 +1835,7 @@
* Can the task run on the task's current CPU? If not then
* migrate the process off to a proper CPU.
*/
- if (new_mask & (1UL << p->cpu)) {
+ if (new_mask & (1UL << task_cpu(p))) {
task_rq_unlock(rq, &flags);
goto out;
}
@@ -1844,7 +1844,7 @@
* it is sufficient to simply update the task's cpu field.
*/
if (!p->array && (p != rq->curr)) {
- p->cpu = __ffs(p->cpus_allowed);
+ set_task_cpu(p, __ffs(p->cpus_allowed));
task_rq_unlock(rq, &flags);
goto out;
}
@@ -1914,18 +1914,18 @@
cpu_dest = __ffs(p->cpus_allowed);
rq_dest = cpu_rq(cpu_dest);
repeat:
- cpu_src = p->cpu;
+ cpu_src = task_cpu(p);
rq_src = cpu_rq(cpu_src);

local_irq_save(flags);
double_rq_lock(rq_src, rq_dest);
- if (p->cpu != cpu_src) {
+ if (task_cpu(p) != cpu_src) {
double_rq_unlock(rq_src, rq_dest);
local_irq_restore(flags);
goto repeat;
}
if (rq_src == rq) {
- p->cpu = cpu_dest;
+ set_task_cpu(p, cpu_dest);
if (p->array) {
deactivate_task(p, rq_src);
activate_task(p, rq_dest);
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