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Subject[PATCH] set_cpus_allowed() for 2.4
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The following patch implements set_cpus_allowed() for stock 2.4 without
the O(1) scheduler.

The calling semantics and behavior remain the same as 2.5's method.

This is to provide a backward-compatible interface, specifically for
those interested in back-porting the new workqueue code to 2.4 -
set_cpus_allowed() seems to be the only nit preventing a straight
drop-in.

Patch is against 2.4.20-pre8 and untested but does compile.

Robert Love

diff -urN linux-2.4.20-pre8/include/linux/sched.h linux/include/linux/sched.h
--- linux-2.4.20-pre8/include/linux/sched.h Mon Sep 30 17:41:22 2002
+++ linux/include/linux/sched.h Tue Oct 1 18:35:28 2002
@@ -163,6 +164,12 @@
extern int start_context_thread(void);
extern int current_is_keventd(void);

+#if CONFIG_SMP
+extern void set_cpus_allowed(struct task_struct *p, unsigned long new_mask);
+#else
+# define set_cpus_allowed(p, new_mask) do { } while (0)
+#endif
+
/*
* The default fd array needs to be at least BITS_PER_LONG,
* as this is the granularity returned by copy_fdset().
diff -urN linux-2.4.20-pre8/kernel/ksyms.c linux/kernel/ksyms.c
--- linux-2.4.20-pre8/kernel/ksyms.c Mon Sep 30 17:41:22 2002
+++ linux/kernel/ksyms.c Tue Oct 1 18:34:41 2002
@@ -451,6 +451,9 @@
EXPORT_SYMBOL(interruptible_sleep_on_timeout);
EXPORT_SYMBOL(schedule);
EXPORT_SYMBOL(schedule_timeout);
+#if CONFIG_SMP
+EXPORT_SYMBOL(set_cpus_allowed);
+#endif
EXPORT_SYMBOL(yield);
EXPORT_SYMBOL(__cond_resched);
EXPORT_SYMBOL(jiffies);
diff -urN linux-2.4.20-pre8/kernel/sched.c linux/kernel/sched.c
--- linux-2.4.20-pre8/kernel/sched.c Mon Sep 30 17:41:22 2002
+++ linux/kernel/sched.c Tue Oct 1 18:54:49 2002
@@ -850,6 +850,46 @@

void scheduling_functions_end_here(void) { }

+#if CONFIG_SMP
+
+/**
+ * set_cpus_allowed() - change a given task's processor affinity
+ * @p: task to bind
+ * @new_mask: bitmask of allowed processors
+ *
+ * Upon return, the task is running on a legal processor. Note the caller
+ * must have a valid reference to the task: it must not exit() prematurely.
+ * This call can sleep; do not hold locks on call.
+ */
+void set_cpus_allowed(struct task_struct *p, unsigned long new_mask)
+{
+ new_mask &= cpu_online_map;
+ BUG_ON(!new_mask);
+
+ p->cpus_allowed = new_mask;
+
+ /*
+ * If the task is on a no-longer-allowed processor, we need to move
+ * it. If the task is not current, then set need_resched and send
+ * its processor an IPI to reschedule.
+ */
+ if (!(p->cpus_runnable & p->cpus_allowed)) {
+ if (p != current) {
+ p->need_resched = 1;
+ smp_send_reschedule(p->processor);
+ }
+ /*
+ * Wait until we are on a legal processor. If the task is
+ * current, then we should be on a legal processor the next
+ * time we reschedule. Otherwise, we need to wait for the IPI.
+ */
+ while (!(p->cpus_runnable & p->cpus_allowed))
+ schedule();
+ }
+}
+
+#endif /* CONFIG_SMP */
+
#ifndef __alpha__

/*
diff -urN linux-2.4.20-pre8/kernel/softirq.c linux/kernel/softirq.c
--- linux-2.4.20-pre8/kernel/softirq.c Mon Sep 30 17:41:22 2002
+++ linux/kernel/softirq.c Tue Oct 1 18:53:01 2002
@@ -368,9 +368,8 @@
sigfillset(&current->blocked);

/* Migrate to the right CPU */
- current->cpus_allowed = 1UL << cpu;
- while (smp_processor_id() != cpu)
- schedule();
+ set_cpus_allowed(current, 1UL << cpu);
+ BUG_ON(smp_processor_id() != cpu);

sprintf(current->comm, "ksoftirqd_CPU%d", bind_cpu);



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