oprofile: adding cpu_buffer_entries()
This is in preparation for changes in the cpu buffer implementation.
Signed-off-by: Robert Richter <robert.richter@amd.com>
diff --git a/drivers/oprofile/cpu_buffer.h b/drivers/oprofile/cpu_buffer.h
index e608976..6055b56 100644
--- a/drivers/oprofile/cpu_buffer.h
+++ b/drivers/oprofile/cpu_buffer.h
@@ -81,6 +81,33 @@
return &cpu_buf->buffer[cpu_buf->tail_pos];
}
+/* "acquire" as many cpu buffer slots as we can */
+static inline
+unsigned long cpu_buffer_entries(struct oprofile_cpu_buffer *b)
+{
+ unsigned long head = b->head_pos;
+ unsigned long tail = b->tail_pos;
+
+ /*
+ * Subtle. This resets the persistent last_task
+ * and in_kernel values used for switching notes.
+ * BUT, there is a small window between reading
+ * head_pos, and this call, that means samples
+ * can appear at the new head position, but not
+ * be prefixed with the notes for switching
+ * kernel mode or a task switch. This small hole
+ * can lead to mis-attribution or samples where
+ * we don't know if it's in the kernel or not,
+ * at the start of an event buffer.
+ */
+ cpu_buffer_reset(b);
+
+ if (head >= tail)
+ return head - tail;
+
+ return head + (b->buffer_size - tail);
+}
+
/* transient events for the CPU buffer -> event buffer */
#define CPU_IS_KERNEL 1
#define CPU_TRACE_BEGIN 2
