ftrace: fix time offset

fix time offset calculations and ordering, plus make code more consistent.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 63 insertions, 21 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c736dd2e068d..8755a4370484 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -120,7 +120,7 @@ static DEFINE_SPINLOCK(ftrace_max_lock);
  * structure. (this way the maximum trace is permanently saved,
  * for later retrieval via /debugfs/tracing/latency_trace)
  */
-static void notrace
+static notrace void
 __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 {
         struct trace_array_cpu *data = tr->data[cpu];
@@ -333,15 +333,16 @@ void unregister_tracer(struct tracer *type)
         mutex_unlock(&trace_types_lock);
 }
 
-void notrace tracing_reset(struct trace_array_cpu *data)
+notrace void tracing_reset(struct trace_array_cpu *data)
 {
         data->trace_idx = 0;
         data->trace_current = head_page(data);
         data->trace_current_idx = 0;
+        data->time_offset = 0;
 }
 
 #ifdef CONFIG_FTRACE
-static void notrace
+static notrace void
 function_trace_call(unsigned long ip, unsigned long parent_ip)
 {
         struct trace_array *tr = &global_trace;
@@ -398,7 +399,7 @@ static void trace_init_cmdlines(void)
 
 notrace void trace_stop_cmdline_recording(void);
 
-static void notrace trace_save_cmdline(struct task_struct *tsk)
+static notrace void trace_save_cmdline(struct task_struct *tsk)
 {
         unsigned map;
         unsigned idx;
@@ -624,6 +625,7 @@ static void *find_next_entry_inc(struct trace_iterator *iter)
                 iter->idx++;
                 iter->next_idx[next_cpu]++;
                 iter->next_page_idx[next_cpu]++;
+
                 if (iter->next_page_idx[next_cpu] >= ENTRIES_PER_PAGE) {
                         struct trace_array_cpu *data = iter->tr->data[next_cpu];
 
@@ -635,19 +637,21 @@ static void *find_next_entry_inc(struct trace_iterator *iter)
                                         data->trace_pages.next;
                 }
         }
+        iter->prev_ent = iter->ent;
+        iter->prev_cpu = iter->cpu;
+
         iter->ent = next;
         iter->cpu = next_cpu;
 
         return next ? iter : NULL;
 }
 
-static void notrace *
-s_next(struct seq_file *m, void *v, loff_t *pos)
+static notrace void *s_next(struct seq_file *m, void *v, loff_t *pos)
 {
         struct trace_iterator *iter = m->private;
-        void *ent;
         void *last_ent = iter->ent;
         int i = (int)*pos;
+        void *ent;
 
         (*pos)++;
 
@@ -693,6 +697,8 @@ static void *s_start(struct seq_file *m, loff_t *pos)
                 iter->ent = NULL;
                 iter->cpu = 0;
                 iter->idx = -1;
+                iter->prev_ent = NULL;
+                iter->prev_cpu = -1;
 
                 for_each_possible_cpu(i) {
                         iter->next_idx[i] = 0;
@@ -752,7 +758,7 @@ seq_print_sym_offset(struct seq_file *m, const char *fmt, unsigned long address)
 # define IP_FMT "%016lx"
 #endif
 
-static void notrace
+static notrace void
 seq_print_ip_sym(struct seq_file *m, unsigned long ip, unsigned long sym_flags)
 {
         if (!ip) {
@@ -769,7 +775,7 @@ seq_print_ip_sym(struct seq_file *m, unsigned long ip, unsigned long sym_flags)
                 seq_printf(m, " <" IP_FMT ">", ip);
 }
 
-static void notrace print_lat_help_header(struct seq_file *m)
+static notrace void print_lat_help_header(struct seq_file *m)
 {
         seq_puts(m, "#                _------=> CPU#            \n");
         seq_puts(m, "#               / _-----=> irqs-off        \n");
@@ -782,14 +788,14 @@ static void notrace print_lat_help_header(struct seq_file *m)
         seq_puts(m, "#     \\   /    |||||   \\   |   /           \n");
 }
 
-static void notrace print_func_help_header(struct seq_file *m)
+static notrace void print_func_help_header(struct seq_file *m)
 {
         seq_puts(m, "#           TASK-PID   CPU#    TIMESTAMP  FUNCTION\n");
         seq_puts(m, "#              | |      |          |         |\n");
 }
 
 
-static void notrace
+static notrace void
 print_trace_header(struct seq_file *m, struct trace_iterator *iter)
 {
         unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
@@ -858,7 +864,7 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter)
         seq_puts(m, "\n");
 }
 
-static void notrace
+static notrace void
 lat_print_generic(struct seq_file *m, struct trace_entry *entry, int cpu)
 {
         int hardirq, softirq;
@@ -895,7 +901,7 @@ lat_print_generic(struct seq_file *m, struct trace_entry *entry, int cpu)
 
 unsigned long preempt_mark_thresh = 100;
 
-static void notrace
+static notrace void
 lat_print_timestamp(struct seq_file *m, unsigned long long abs_usecs,
                     unsigned long rel_usecs)
 {
@@ -910,7 +916,7 @@ lat_print_timestamp(struct seq_file *m, unsigned long long abs_usecs,
 
 static const char state_to_char[] = TASK_STATE_TO_CHAR_STR;
 
-static void notrace
+static notrace void
 print_lat_fmt(struct seq_file *m, struct trace_iterator *iter,
               unsigned int trace_idx, int cpu)
 {
@@ -966,20 +972,50 @@ print_lat_fmt(struct seq_file *m, struct trace_iterator *iter,
         }
 }
 
-static void notrace
+static notrace void sync_time_offset(struct trace_iterator *iter)
+{
+        struct trace_array_cpu *prev_array, *array;
+        struct trace_entry *prev_entry, *entry;
+        cycle_t prev_t, t;
+
+        entry = iter->ent;
+        prev_entry = iter->prev_ent;
+        if (!prev_entry)
+                return;
+
+        prev_array = iter->tr->data[iter->prev_cpu];
+        array = iter->tr->data[iter->cpu];
+
+        prev_t = prev_entry->t + prev_array->time_offset;
+        t = entry->t + array->time_offset;
+
+        /*
+         * If time goes backwards we increase the offset of
+         * the current array, to not have observable time warps.
+         * This will quickly synchronize the time offsets of
+         * multiple CPUs:
+         */
+        if (t < prev_t)
+                array->time_offset += prev_t - t;
+}
+
+static notrace void
 print_trace_fmt(struct seq_file *m, struct trace_iterator *iter)
 {
         unsigned long sym_flags = (trace_flags & TRACE_ITER_SYM_MASK);
-        struct trace_entry *entry = iter->ent;
+        struct trace_entry *entry;
         unsigned long usec_rem;
         unsigned long long t;
         unsigned long secs;
         char *comm;
         int S;
 
+        sync_time_offset(iter);
+        entry = iter->ent;
+
         comm = trace_find_cmdline(iter->ent->pid);
 
-        t = ns2usecs(entry->t);
+        t = ns2usecs(entry->t + iter->tr->data[iter->cpu]->time_offset);
         usec_rem = do_div(t, 1000000ULL);
         secs = (unsigned long)t;
 
@@ -1158,7 +1194,7 @@ static int tracing_lt_open(struct inode *inode, struct file *file)
 }
 
 
-static void notrace *
+static notrace void *
 t_next(struct seq_file *m, void *v, loff_t *pos)
 {
         struct tracer *t = m->private;
@@ -1374,8 +1410,7 @@ tracing_ctrl_read(struct file *filp, char __user *ubuf,
         int r;
 
         r = sprintf(buf, "%ld\n", tr->ctrl);
-        return simple_read_from_buffer(ubuf, cnt, ppos,
-                                       buf, r);
+        return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
 }
 
 static ssize_t
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index cc1d34b8b771..5df8ff2b84a7 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -56,6 +56,8 @@ struct trace_array_cpu {
         void                    *trace_current;
         struct list_head        trace_pages;
         atomic_t                disabled;
+        cycle_t                 time_offset;
+
         /* these fields get copied into max-trace: */
         unsigned                trace_current_idx;
         unsigned long           trace_idx;
@@ -114,14 +116,19 @@ struct tracer {
 struct trace_iterator {
         struct trace_array      *tr;
         struct tracer           *trace;
+
         struct trace_entry      *ent;
+        int                     cpu;
+
+        struct trace_entry      *prev_ent;
+        int                     prev_cpu;
+
         unsigned long           iter_flags;
         loff_t                  pos;
         unsigned long           next_idx[NR_CPUS];
         struct list_head        *next_page[NR_CPUS];
         unsigned                next_page_idx[NR_CPUS];
         long                    idx;
-        int                     cpu;
 };
 
 void notrace tracing_reset(struct trace_array_cpu *data);