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>

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index b1a0068..9e6052b 100644 (file)
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -118,8 +118,11 @@ unsigned long ring_buffer_overruns(struct ring_buffer *buffer);
 unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu);
 unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu);
 
-u64 ring_buffer_time_stamp(int cpu);
-void ring_buffer_normalize_time_stamp(int cpu, u64 *ts);
+u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu);
+void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
+                                     int cpu, u64 *ts);
+void ring_buffer_set_clock(struct ring_buffer *buffer,
+                          u64 (*clock)(void));
 
 size_t ring_buffer_page_len(void *page);
 

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 58128ad..bbf5192 100644 (file)
--- 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 8f89690..3be2f78 100644 (file)
--- 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