[PATCH] scheduler: migration tasks startup

From: Erich Focht (efocht@ess.nec.de)
Date: Wed Mar 06 2002 - 05:32:46 EST

Hi,

we encountered problems with the initial distribution of the
migration_tasks across the CPUs. Machines with 16 and more CPUs
sometimes won't boot. Here is a fix which works reliably:
- all migration_tasks are started on CPU#0,
- migration_task #0 is used to migrate the others to their destination,
- synchronization with migration_mask isn't needed any more.

Thanks,
best regards,
Erich

diff -urN 2.5.6-pre1-fix/kernel/sched.c 2.5.6-pre1-fix2/kernel/sched.c
--- 2.5.6-pre1-fix/kernel/sched.c Thu Feb 28 19:14:29 2002
+++ 2.5.6-pre1-fix2/kernel/sched.c Wed Mar 6 11:28:59 2002
@@ -1557,8 +1557,9 @@
 
 static volatile unsigned long migration_mask;
 
-static int migration_thread(void * unused)
+static int migration_thread(void * bind_cpu)
 {
+ int cpu = cpu_logical_map((int) (long) bind_cpu);
         struct sched_param param = { sched_priority: 99 };
         runqueue_t *rq;
         int ret;
@@ -1566,33 +1567,19 @@
         daemonize();
         sigfillset(&current->blocked);
         set_fs(KERNEL_DS);
- ret = setscheduler(0, SCHED_FIFO, &param);
 
         /*
- * We have to migrate manually - there is no migration thread
- * to do this for us yet :-)
- *
- * We use the following property of the Linux scheduler. At
- * this point no other task is running, so by keeping all
- * migration threads running, the load-balancer will distribute
- * them between all CPUs equally. At that point every migration
- * task binds itself to the current CPU.
+ * The first migration task is started on CPU #0. This one can migrate
+ * the tasks to their destination CPUs.
          */
-
- /* wait for all migration threads to start up. */
- while (!migration_mask)
- yield();
-
- for (;;) {
- preempt_disable();
- if (test_and_clear_bit(smp_processor_id(), &migration_mask))
- current->cpus_allowed = 1 << smp_processor_id();
- if (test_thread_flag(TIF_NEED_RESCHED))
- schedule();
- if (!migration_mask)
- break;
- preempt_enable();
+ if (cpu != 0) {
+ while (!cpu_rq(cpu_logical_map(0))->migration_thread)
+ yield();
+ set_cpus_allowed(current, 1UL << cpu);
         }
+ printk("migration_task %d on cpu=%d\n",cpu,smp_processor_id());
+ ret = setscheduler(0, SCHED_FIFO, &param);
+
         rq = this_rq();
         rq->migration_thread = current;
         preempt_enable();
@@ -1651,17 +1638,15 @@
 {
         int cpu;
 
+ current->cpus_allowed = 1UL << cpu_logical_map(0);
         for (cpu = 0; cpu < smp_num_cpus; cpu++)
- if (kernel_thread(migration_thread, NULL,
+ if (kernel_thread(migration_thread, (void *) (long) cpu,
                                 CLONE_FS | CLONE_FILES | CLONE_SIGNAL) < 0)
                         BUG();
-
- migration_mask = (1 << smp_num_cpus) - 1;
+ current->cpus_allowed = -1L;
 
         for (cpu = 0; cpu < smp_num_cpus; cpu++)
                 while (!cpu_rq(cpu)->migration_thread)
                         schedule_timeout(2);
- if (migration_mask)
- BUG();
 }
 #endif

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This archive was generated by hypermail 2b29 : Thu Mar 07 2002 - 21:00:54 EST