start tracer disabled

Hi,

this tiny patch adds a config option to I-pipe to allow starting the system with the tracer compiled in but disabled. You can then enabled it on demand via /proc/ipipe/tracer/enable. This saves a bit time when booting low-end boxes (I wonder why I didn't hacked this earlier...).

Jan
plain text document attachment (tracer-default-off.patch)
Index: linux-2.6.17.8/kernel/ipipe/Kconfig
===================================================================

kernel/ipipe/Kconfig +15 -1

@@ -6,7 +6,7 @@ config IPIPE
 	  compiled in.
 
 config IPIPE_TRACE
- 	bool "Latency Tracing"
+	bool "Latency tracing"
 	depends on IPIPE && PROC_FS
 	select FRAME_POINTER
 	default n

@@ -18,6 +18,15 @@ config IPIPE_TRACE
 	  in-kernel tracing API. The collected data and runtime control
 	  is available via /proc/ipipe/trace/*.
 
+config IPIPE_TRACE_ENABLE
+	bool "Enable tracing on boot"
+	depends on IPIPE_TRACE
+	default y
+	---help---
+	  Disable this option if you want to arm the tracer after booting
+	  manually ("echo 1 > /proc/ipipe/tracer/enable"). This can reduce
+	  boot time on slow embedded devices due to the tracer overhead.
+
 config IPIPE_TRACE_IRQSOFF
 	bool "Trace IRQs-off times"
 	depends on IPIPE_TRACE

@@ -44,3 +53,8 @@ config IPIPE_TRACE_VMALLOC
 	  enabled. This can help to start systems that are low on memory,
 	  but it slightly degrades overall performance. Try this option
 	  when a traced kernel hangs unexpectedly at boot time.
+
+config IPIPE_TRACE_ENABLE_VALUE
+	int
+	default 0 if !IPIPE_TRACE_ENABLE
+	default 1 if IPIPE_TRACE_ENABLE

Index: linux-2.6.17.8/kernel/ipipe/tracer.c
===================================================================

kernel/ipipe/tracer.c +2 -2

@@ -105,7 +105,7 @@ enum ipipe_trace_type
 static struct ipipe_trace_path *trace_paths[NR_CPUS];
 
 #else /* !CONFIG_IPIPE_TRACE_VMALLOC */
-#define IPIPE_DEFAULT_TRACE_STATE   1
+#define IPIPE_DEFAULT_TRACE_STATE   CONFIG_IPIPE_TRACE_ENABLE_VALUE
 
 static struct ipipe_trace_path trace_paths[NR_CPUS][IPIPE_TRACE_PATHS] =
 	{ [0 ... NR_CPUS-1] =

@@ -1217,7 +1217,7 @@ void __init __ipipe_init_tracer(void)
 			trace_paths[cpu][path].end   = -1;
 		}
 	}
-	ipipe_trace_enable = 1;
+	ipipe_trace_enable = CONFIG_IPIPE_TRACE_ENABLE_VALUE;
 #endif /* CONFIG_IPIPE_TRACE_VMALLOC */
 
 	trace_dir = create_proc_entry("trace", S_IFDIR, ipipe_proc_root);

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