4 files changed, 39 insertions, 13 deletions

diff --git a/include/litmus/sched_mc.h b/include/litmus/sched_mc.h
index 740cc11be5d7..8cdec04c64df 100644
--- a/include/litmus/sched_mc.h
+++ b/include/litmus/sched_mc.h
@@ -31,6 +31,14 @@ struct mc_data {
         struct mc_job mc_job;
 };
 
+/* Leave a CPU free for tracing stuff */
+#if CONFIG_FTRACE_CPU != NO_CPU
+extern struct cpumask rt_mask;
+#define for_each_rt_cpu(cpu) for_each_cpu((cpu), &rt_mask)
+#else
+#define for_each_rt_cpu(cpu) for_each_online_cpu(cpu)
+#endif
+
 #define tsk_mc_data(t)   (tsk_rt(t)->mc_data)
 #define tsk_mc_crit(t)   (tsk_mc_data(t)->mc_task.crit)
 #define is_ghost(t)      (tsk_mc_data(t)->mc_job.is_ghost)
diff --git a/litmus/Kconfig b/litmus/Kconfig
index d629a2843584..20610fdf9a54 100644
--- a/litmus/Kconfig
+++ b/litmus/Kconfig
@@ -83,8 +83,15 @@ config PLUGIN_MC_REDIRECT
          Allow processors to send work involving global state to the
          release-master cpu in order to avoid excess overheads during
          partitioned decisions.
-endmenu
 
+config FTRACE_CPU
+       int "CPU for Tracing"
+       depends on PLUGIN_MC
+       default -1
+       help
+         Keep one CPU free for the tasks which trace and flush
+         scheduling and overhead data.
+endmenu
 endmenu
 
 menu "Real-Time Synchronization"
diff --git a/litmus/sched_mc.c b/litmus/sched_mc.c
index 53c24ac2172c..8828919dfcf2 100644
--- a/litmus/sched_mc.c
+++ b/litmus/sched_mc.c
@@ -60,6 +60,8 @@ DEFINE_PER_CPU(struct cpu_entry, cpus);
 static int interrupt_cpu;
 #endif
 
+struct cpumask rt_mask;
+
 #define domain_data(dom)  (container_of(dom, struct domain_data, domain))
 #define is_global(dom)    (domain_data(dom)->heap)
 #define is_global_task(t) (is_global(get_task_domain(t)))
@@ -350,7 +352,7 @@ static void fix_global_levels(void)
         struct task_struct *t;
 
         STRACE("Fixing global levels\n");
-        for_each_online_cpu(c) {
+        for_each_rt_cpu(c) {
                 e = &per_cpu(cpus, c);
                 raw_spin_lock(&e->redir_lock);
                 list_for_each_safe(pos, safe, &e->redir) {
@@ -377,6 +379,7 @@ static void link_task_to_cpu(struct cpu_entry *entry, struct task_struct *task)
         TRACE_MC_TASK(task, "Linking to P%d\n", entry->cpu);
         BUG_ON(task && tsk_rt(task)->linked_on != entry->cpu);
         BUG_ON(task && is_ghost(task));
+        BUG_ON(CONFIG_FTRACE_CPU == entry->cpu);
 
         if (task){
                 set_rt_flags(task, RT_F_RUNNING);
@@ -892,6 +895,10 @@ static struct task_struct* mc_schedule(struct task_struct* prev)
         int i, out_of_time, sleep, preempt, exists, blocks, global, lower;
         struct task_struct *dtask = NULL, *ready_task = NULL, *next = NULL;
 
+        /* Give FTRACE a CPU to run on */
+        if (CONFIG_FTRACE_CPU == entry->cpu)
+                return NULL;
+
         local_irq_save(flags);
 
         /* Litmus gave up because it couldn't access the stack of the CPU
@@ -1075,7 +1082,7 @@ static long mc_activate_plugin(void)
 #endif
 #endif
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 BUG_ON(NR_CPUS <= n);
                 dom = per_cpu(cpus, cpu).crit_entries[CRIT_LEVEL_A].domain;
                 dom_data = domain_data(dom);
@@ -1150,7 +1157,7 @@ static void init_global_domain(struct domain_data *dom_data, enum crit_level lev
         dom_data->heap = heap;
         bheap_init(heap);
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 entry = &per_cpu(cpus, cpu);
                 node = &nodes[cpu];
                 ce = &entry->crit_entries[level];
@@ -1199,7 +1206,11 @@ static int __init init_mc(void)
         raw_spinlock_t *a_dom_lock, *b_dom_lock, *c_dom_lock; /* For lock debugger */
         struct ce_dom_data *ce_data;
 
-        for_each_online_cpu(cpu) {
+#if CONFIG_FTRACE_CPU != NO_CPU
+        cpumask_xor(&rt_mask, cpu_online_mask, cpumask_of(CONFIG_FTRACE_CPU));
+#endif
+
+        for_each_rt_cpu(cpu) {
                 entry = &per_cpu(cpus, cpu);
 
                 /* CPU */
diff --git a/litmus/sched_mc_ce.c b/litmus/sched_mc_ce.c
index af02dfdbb523..d9be4d14e76c 100644
--- a/litmus/sched_mc_ce.c
+++ b/litmus/sched_mc_ce.c
@@ -565,7 +565,7 @@ static int cancel_all_timers(void)
 
         TRACE("cancel all timers\n");
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 dom = get_domain_for(cpu);
                 ce_data = dom->data;
                 ce_data->should_schedule = NULL;
@@ -596,7 +596,7 @@ static void arm_all_timers(void)
 
         TRACE("arm all timers\n");
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 dom = get_domain_for(cpu);
                 ce_data = dom->data;
                 pid_table = get_pid_table(cpu);
@@ -655,7 +655,7 @@ long mc_ce_activate_plugin_common(void)
         }
 #endif
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 dom = get_domain_for(cpu);
                 ce_data = dom->data;
                 ce_data->scheduled = NULL;
@@ -677,7 +677,7 @@ static long mc_ce_activate_plugin(void)
         int cpu, n = 0;
         long ret;
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 BUG_ON(NR_CPUS <= n);
                 our_domains[cpu] = &per_cpu(_mc_ce_doms, cpu);
                 n++;
@@ -695,7 +695,7 @@ static void clear_pid_entries(void)
         struct ce_pid_table *pid_table = NULL;
         int cpu, entry;
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 pid_table = get_pid_table(cpu);
                 pid_table->num_pid_entries = 0;
                 pid_table->cycle_time = 0;
@@ -716,7 +716,7 @@ long mc_ce_deactivate_plugin_common(void)
 {
         int cpu;
         cancel_all_timers();
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 per_cpu(domains, cpu) = NULL;
         }
         return 0;
@@ -746,7 +746,7 @@ static int __init init_sched_mc_ce(void)
         struct domain *dom;
         int cpu, err;
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 per_cpu(domains, cpu) = NULL;
                 ce_lock = &per_cpu(_mc_ce_dom_locks, cpu);
                 raw_spin_lock_init(ce_lock);
@@ -860,7 +860,7 @@ static int proc_read_ce_file(char *page, char **start, off_t off, int count,
                 goto out;
         }
 
-        for_each_online_cpu(cpu) {
+        for_each_rt_cpu(cpu) {
                 pid_table = get_pid_table(cpu);
                 for (t = 0; t < pid_table->num_pid_entries; ++t) {
                         err = write_pid_entry(page + n, count - n,