Solution for the potential deadlock when needing to flush the profiling

buffer during a timer event that interrupted a kernel function: We do
now flush the buffer as soon as it is 70% full, *if* we didn't interrupt
a kernel function. When the buffer runs full and we still haven't hit a
user function, we drop the tick. The number of dropped ticks is recorded
and sent to the debugger with the next update message.
Reverted the previous partial solution (the temporary disabling of
profiling while in debugger support code).


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27658 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/user_debugger.h

@@ -15,9 +15,10 @@
 
 
 // limits
-#define B_DEBUG_MAX_PROFILE_FUNCTIONS	100000
-#define B_DEBUG_MIN_PROFILE_INTERVAL	100			/* in us */
-#define B_DEBUG_STACK_TRACE_DEPTH		5
+#define B_DEBUG_MAX_PROFILE_FUNCTIONS			100000
+#define B_DEBUG_MIN_PROFILE_INTERVAL			100			/* in us */
+#define B_DEBUG_STACK_TRACE_DEPTH				5
+#define	B_DEBUG_PROFILE_BUFFER_FLUSH_THRESHOLD	70			/* in % */
 
 
 struct function_profile_info;
@@ -84,15 +85,18 @@ struct thread_debug_info {
 			// sample buffer
 		int32			max_samples;
 			// maximum number of samples the buffer can hold
+		int32			flush_threshold;
+			// number of sample when the buffer is flushed (if possible)
 		int32			sample_count;
 			// number of samples the buffer currently holds
 		int32			stack_depth;
 			// number of return addresses to record per timer interval
+		int32			dropped_ticks;
+			// number of ticks that had to be dropped when the sample buffer was
+			// full and couldn't be flushed
 		int32			image_event;
 			// number of the image event when the first sample was written into
 			// the buffer
-		int32			disabled;
-			// if > 0, profiling is temporarily disabled for the thread
 		bool			buffer_full;
 			// indicates that the sample buffer is full
 		union {