ring-buffer: add api to allow a tracer to change clock source

This patch adds a new function called ring_buffer_set_clock that
allows a tracer to assign its own clock source to the buffer.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

2 files changed, 52 insertions, 34 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 58128ad2fde0..bbf51922a8ca 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -180,29 +180,6 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
 
 #include "trace.h"
 
-/* Up this if you want to test the TIME_EXTENTS and normalization */
-#define DEBUG_SHIFT 0
-
-u64 ring_buffer_time_stamp(int cpu)
-{
-        u64 time;
-
-        preempt_disable_notrace();
-        /* shift to debug/test normalization and TIME_EXTENTS */
-        time = trace_clock_local() << DEBUG_SHIFT;
-        preempt_enable_no_resched_notrace();
-
-        return time;
-}
-EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
-
-void ring_buffer_normalize_time_stamp(int cpu, u64 *ts)
-{
-        /* Just stupid testing the normalize function and deltas */
-        *ts >>= DEBUG_SHIFT;
-}
-EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
-
 #define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
 #define RB_ALIGNMENT            4U
 #define RB_MAX_SMALL_DATA       28
@@ -374,6 +351,7 @@ struct ring_buffer {
 #ifdef CONFIG_HOTPLUG_CPU
         struct notifier_block           cpu_notify;
 #endif
+        u64                             (*clock)(void);
 };
 
 struct ring_buffer_iter {
@@ -394,6 +372,30 @@ struct ring_buffer_iter {
                 _____ret;                                       \
         })
 
+/* Up this if you want to test the TIME_EXTENTS and normalization */
+#define DEBUG_SHIFT 0
+
+u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
+{
+        u64 time;
+
+        preempt_disable_notrace();
+        /* shift to debug/test normalization and TIME_EXTENTS */
+        time = buffer->clock() << DEBUG_SHIFT;
+        preempt_enable_no_resched_notrace();
+
+        return time;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
+
+void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
+                                      int cpu, u64 *ts)
+{
+        /* Just stupid testing the normalize function and deltas */
+        *ts >>= DEBUG_SHIFT;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
+
 /**
  * check_pages - integrity check of buffer pages
  * @cpu_buffer: CPU buffer with pages to test
@@ -569,6 +571,7 @@ struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
 
         buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
         buffer->flags = flags;
+        buffer->clock = trace_clock_local;
 
         /* need at least two pages */
         if (buffer->pages == 1)
@@ -645,6 +648,12 @@ ring_buffer_free(struct ring_buffer *buffer)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_free);
 
+void ring_buffer_set_clock(struct ring_buffer *buffer,
+                           u64 (*clock)(void))
+{
+        buffer->clock = clock;
+}
+
 static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
 
 static void
@@ -1191,7 +1200,7 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
                         cpu_buffer->tail_page = next_page;
 
                         /* reread the time stamp */
-                        *ts = ring_buffer_time_stamp(cpu_buffer->cpu);
+                        *ts = ring_buffer_time_stamp(buffer, cpu_buffer->cpu);
                         cpu_buffer->tail_page->page->time_stamp = *ts;
                 }
 
@@ -1334,7 +1343,7 @@ rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
         if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
                 return NULL;
 
-        ts = ring_buffer_time_stamp(cpu_buffer->cpu);
+        ts = ring_buffer_time_stamp(cpu_buffer->buffer, cpu_buffer->cpu);
 
         /*
          * Only the first commit can update the timestamp.
@@ -2051,7 +2060,8 @@ rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
         case RINGBUF_TYPE_DATA:
                 if (ts) {
                         *ts = cpu_buffer->read_stamp + event->time_delta;
-                        ring_buffer_normalize_time_stamp(cpu_buffer->cpu, ts);
+                        ring_buffer_normalize_time_stamp(buffer,
+                                                         cpu_buffer->cpu, ts);
                 }
                 return event;
 
@@ -2112,7 +2122,8 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
         case RINGBUF_TYPE_DATA:
                 if (ts) {
                         *ts = iter->read_stamp + event->time_delta;
-                        ring_buffer_normalize_time_stamp(cpu_buffer->cpu, ts);
+                        ring_buffer_normalize_time_stamp(buffer,
+                                                         cpu_buffer->cpu, ts);
                 }
                 return event;
 
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8f89690230e6..3be2f788e10d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -155,13 +155,6 @@ ns2usecs(cycle_t nsec)
         return nsec;
 }
 
-cycle_t ftrace_now(int cpu)
-{
-        u64 ts = ring_buffer_time_stamp(cpu);
-        ring_buffer_normalize_time_stamp(cpu, &ts);
-        return ts;
-}
-
 /*
  * The global_trace is the descriptor that holds the tracing
  * buffers for the live tracing. For each CPU, it contains
@@ -178,6 +171,20 @@ static struct trace_array	global_trace;
 
 static DEFINE_PER_CPU(struct trace_array_cpu, global_trace_cpu);
 
+cycle_t ftrace_now(int cpu)
+{
+        u64 ts;
+
+        /* Early boot up does not have a buffer yet */
+        if (!global_trace.buffer)
+                return trace_clock_local();
+
+        ts = ring_buffer_time_stamp(global_trace.buffer, cpu);
+        ring_buffer_normalize_time_stamp(global_trace.buffer, cpu, &ts);
+
+        return ts;
+}
+
 /*
  * The max_tr is used to snapshot the global_trace when a maximum
  * latency is reached. Some tracers will use this to store a maximum