[PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

[PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

[Lai Jiangshan]

When I am writing userspace tools for ftrace, I found
RB_MAX_SMALL_DATA is too small, some events waste an 'u32'
to save the actually length.

This fix will break previous userspace tools,
so complaints are also welcome.
--------------

Subject: [PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

Impact: save memory in ring_buffer

I found 28bytes for an event data is sometimes too small,
it will waste an 'u32' to save the actually length for
events which data size > 28.

'len=5' in the next logs means the event size is sizeof(u32)*5=20 bytes,
it includes event head and event data. This logs are collected
in 32bits system.

syscall tracer:
time_stamp=391042354662405, len=10
time_stamp=391042354679741, len=5
time_stamp=391042354686278, len=9
time_stamp=391042354691465, len=5
time_stamp=391042354695348, len=9
time_stamp=391042354698631, len=5
time_stamp=391042354703472, len=7
time_stamp=391042354756153, len=5
time_stamp=391042354766952, len=7
time_stamp=391042354790733, len=5
time_stamp=391042355124535, len=10
time_stamp=391042355136474, len=5
time_stamp=391042355141883, len=9
time_stamp=391042355146048, len=5
time_stamp=391042355149837, len=9
time_stamp=391042355152939, len=5
time_stamp=391042355157944, len=7
time_stamp=391042355194303, len=5
time_stamp=391042355200947, len=10
time_stamp=391042355690428, len=5
time_stamp=391042355700443, len=9

kmemtrace tracer:
time_stamp=391116237929771, len=6
time_stamp=391116237935560, len=6
time_stamp=391116237937269, len=6
time_stamp=391116649408762, len=11
time_stamp=391116649415541, len=11
time_stamp=391116649421702, len=11
time_stamp=391116649428121, len=6
time_stamp=391116649612696, len=6
time_stamp=391116649616327, len=6
time_stamp=391116649948694, len=11
time_stamp=391116650097324, len=11
time_stamp=391116650111344, len=11
time_stamp=391116650116344, len=6
time_stamp=391116656377385, len=11
time_stamp=391116656383258, len=11
time_stamp=391116656399858, len=11
time_stamp=391116656406757, len=6
time_stamp=391116657165045, len=11
time_stamp=391116657172126, len=11
time_stamp=391116657178716, len=11
time_stamp=391116657185031, len=6
time_stamp=391116657268110, len=6
time_stamp=391116657273307, len=6
time_stamp=391116657275341, len=6
time_stamp=391116657276638, len=6
time_stamp=391116657283869, len=6

sched_switch tracer:
time_stamp=391250280621660, len=9
time_stamp=391250281277013, len=9
time_stamp=391250281328332, len=9
time_stamp=391250600954274, len=9
time_stamp=391250601092171, len=9
time_stamp=391250601276548, len=9
time_stamp=391250601342968, len=9
time_stamp=391250601616099, len=9
time_stamp=391250602099709, len=9
time_stamp=391250603414452, len=9
time_stamp=391250605580652, len=9
time_stamp=391250605598567, len=9

function_graph tracer:
time_stamp=391216875265827, len=11
time_stamp=391216875270031, len=5
time_stamp=391216875272943, len=5
time_stamp=391216875275169, len=5
time_stamp=391216875279253, len=11
time_stamp=391216875282684, len=5
time_stamp=391216875291602, len=11
time_stamp=391216875294898, len=5

After this fix applied, function_graph tracer:

time_stamp=395685660789931, len=5
time_stamp=395685660792751, len=10
time_stamp=395685660795807, len=5
time_stamp=395685660798260, len=10
time_stamp=395685660801224, len=10
time_stamp=395685660804164, len=10
time_stamp=395685660807068, len=5
time_stamp=395685660809314, len=5
time_stamp=395685660812001, len=10
time_stamp=395685660815589, len=10
time_stamp=395685660823151, len=5
time_stamp=395685660825215, len=5
time_stamp=395685660827697, len=5
time_stamp=395685660829589, len=10
time_stamp=395685660833558, len=10
time_stamp=395685660836630, len=10

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 3d3ab00..5298ee1 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -13,7 +13,7 @@ struct ring_buffer_iter;
  */
 struct ring_buffer_event {
 	kmemcheck_define_bitfield(bitfield, {
-		u32		type:2, len:3, time_delta:27;
+		u32		type:2, len:4, time_delta:26;
 	});
 
 	u32		array[];
@@ -31,7 +31,7 @@ struct ring_buffer_event {
  *				  everything else same as RINGBUF_TYPE_DATA
  *
  * @RINGBUF_TYPE_TIME_EXTEND:	Extend the time delta
- *				 array[0] = time delta (28 .. 59)
+ *				 array[0] = time delta (27 .. 58)
  *				 size = 8 bytes
  *
  * @RINGBUF_TYPE_TIME_STAMP:	Sync time stamp with external clock
@@ -64,7 +64,7 @@ void *ring_buffer_event_data(struct ring_buffer_event *event);
  * ring_buffer_event_time_delta - return the delta timestamp of the event
  * @event: the event to get the delta timestamp of
  *
- * The delta timestamp is the 27 bit timestamp since the last event.
+ * The delta timestamp is the 26 bit timestamp since the last event.
  */
 static inline unsigned
 ring_buffer_event_time_delta(struct ring_buffer_event *event)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index e773c57..33bdde2 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -183,7 +183,7 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
 
 #define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
 #define RB_ALIGNMENT		4U
-#define RB_MAX_SMALL_DATA	28
+#define RB_MAX_SMALL_DATA	60
 
 enum {
 	RB_LEN_TIME_EXTEND = 8,
@@ -285,7 +285,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
 #define for_each_buffer_cpu(buffer, cpu)		\
 	for_each_cpu(cpu, buffer->cpumask)
 
-#define TS_SHIFT	27
+#define TS_SHIFT	26
 #define TS_MASK		((1ULL << TS_SHIFT) - 1)
 #define TS_DELTA_TEST	(~TS_MASK)
 
@@ -330,7 +330,7 @@ static void free_buffer_page(struct buffer_page *bpage)
 }
 
 /*
- * We need to fit the time_stamp delta into 27 bits.
+ * We need to fit the time_stamp delta into 26 bits.
  */
 static inline int test_time_stamp(u64 delta)
 {
@@ -1299,7 +1299,7 @@ rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
 	static int once;
 	int ret;
 
-	if (unlikely(*delta > (1ULL << 59) && !once++)) {
+	if (unlikely(*delta > (1ULL << 58) && !once++)) {
 		printk(KERN_WARNING "Delta way too big! %llu"
 		       " ts=%llu write stamp = %llu\n",
 		       (unsigned long long)*delta,

Re: [PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

[Steven Rostedt]

On Mon, 2009-04-13 at 11:00 +0800, Lai Jiangshan wrote:
> When I am writing userspace tools for ftrace, I found
> RB_MAX_SMALL_DATA is too small, some events waste an 'u32'
> to save the actually length.

Although I like the idea, I want to look at something else.

2^27 is: 134,217,728
2^26 is: 67,108,864

That is the count in nanoseconds. Thus we go from 134 millisecs to 67
millisecs before we must add an extended counter.

I guess that is not an issue, since 67ms is still quite big. For sparse
tracing, it could add more extended counters where none were needed. But
this I doubt this is an issue.

> 
> This fix will break previous userspace tools,
> so complaints are also welcome.
> --------------
> 
> Subject: [PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA
> 
> Impact: save memory in ring_buffer
> 
> I found 28bytes for an event data is sometimes too small,
> it will waste an 'u32' to save the actually length for
> events which data size > 28.
> 
> 'len=5' in the next logs means the event size is sizeof(u32)*5=20 bytes,
> it includes event head and event data. This logs are collected
> in 32bits system.
> 
> syscall tracer:
> time_stamp=391042354662405, len=10
> time_stamp=391042354679741, len=5
> time_stamp=391042354686278, len=9
> time_stamp=391042354691465, len=5
> time_stamp=391042354695348, len=9
> time_stamp=391042354698631, len=5
> time_stamp=391042354703472, len=7
> time_stamp=391042354756153, len=5
> time_stamp=391042354766952, len=7
> time_stamp=391042354790733, len=5
> time_stamp=391042355124535, len=10
> time_stamp=391042355136474, len=5
> time_stamp=391042355141883, len=9
> time_stamp=391042355146048, len=5
> time_stamp=391042355149837, len=9
> time_stamp=391042355152939, len=5
> time_stamp=391042355157944, len=7
> time_stamp=391042355194303, len=5
> time_stamp=391042355200947, len=10
> time_stamp=391042355690428, len=5
> time_stamp=391042355700443, len=9
> 
> kmemtrace tracer:
> time_stamp=391116237929771, len=6
> time_stamp=391116237935560, len=6
> time_stamp=391116237937269, len=6
> time_stamp=391116649408762, len=11
> time_stamp=391116649415541, len=11
> time_stamp=391116649421702, len=11
> time_stamp=391116649428121, len=6
> time_stamp=391116649612696, len=6
> time_stamp=391116649616327, len=6
> time_stamp=391116649948694, len=11
> time_stamp=391116650097324, len=11
> time_stamp=391116650111344, len=11
> time_stamp=391116650116344, len=6
> time_stamp=391116656377385, len=11
> time_stamp=391116656383258, len=11
> time_stamp=391116656399858, len=11
> time_stamp=391116656406757, len=6
> time_stamp=391116657165045, len=11
> time_stamp=391116657172126, len=11
> time_stamp=391116657178716, len=11
> time_stamp=391116657185031, len=6
> time_stamp=391116657268110, len=6
> time_stamp=391116657273307, len=6
> time_stamp=391116657275341, len=6
> time_stamp=391116657276638, len=6
> time_stamp=391116657283869, len=6
> 
> sched_switch tracer:
> time_stamp=391250280621660, len=9
> time_stamp=391250281277013, len=9
> time_stamp=391250281328332, len=9
> time_stamp=391250600954274, len=9
> time_stamp=391250601092171, len=9
> time_stamp=391250601276548, len=9
> time_stamp=391250601342968, len=9
> time_stamp=391250601616099, len=9
> time_stamp=391250602099709, len=9
> time_stamp=391250603414452, len=9
> time_stamp=391250605580652, len=9
> time_stamp=391250605598567, len=9
> 
> function_graph tracer:
> time_stamp=391216875265827, len=11
> time_stamp=391216875270031, len=5
> time_stamp=391216875272943, len=5
> time_stamp=391216875275169, len=5
> time_stamp=391216875279253, len=11
> time_stamp=391216875282684, len=5
> time_stamp=391216875291602, len=11
> time_stamp=391216875294898, len=5
> 
> After this fix applied, function_graph tracer:
> 
> time_stamp=395685660789931, len=5
> time_stamp=395685660792751, len=10
> time_stamp=395685660795807, len=5
> time_stamp=395685660798260, len=10
> time_stamp=395685660801224, len=10
> time_stamp=395685660804164, len=10
> time_stamp=395685660807068, len=5
> time_stamp=395685660809314, len=5
> time_stamp=395685660812001, len=10
> time_stamp=395685660815589, len=10
> time_stamp=395685660823151, len=5
> time_stamp=395685660825215, len=5
> time_stamp=395685660827697, len=5
> time_stamp=395685660829589, len=10
> time_stamp=395685660833558, len=10
> time_stamp=395685660836630, len=10
> 
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index 3d3ab00..5298ee1 100644
> --- a/include/linux/ring_buffer.h
> +++ b/include/linux/ring_buffer.h
> @@ -13,7 +13,7 @@ struct ring_buffer_iter;
>   */
>  struct ring_buffer_event {
>  	kmemcheck_define_bitfield(bitfield, {
> -		u32		type:2, len:3, time_delta:27;
> +		u32		type:2, len:4, time_delta:26;
>  	});
>  
>  	u32		array[];
> @@ -31,7 +31,7 @@ struct ring_buffer_event {
>   *				  everything else same as RINGBUF_TYPE_DATA
>   *
>   * @RINGBUF_TYPE_TIME_EXTEND:	Extend the time delta
> - *				 array[0] = time delta (28 .. 59)
> + *				 array[0] = time delta (27 .. 58)
>   *				 size = 8 bytes

Unfortunately, this changes the API to userspace. For those parsers that
do this in binary. I think the answer is, before we add this, we export
the format of the ring buffer headers just like we do for other formats.
This way, a user tool can default to the old way if the format file does
not exist, and can know the current format with the file.

I'll work on adding that format file sometime this week.

-- Steve

>   *
>   * @RINGBUF_TYPE_TIME_STAMP:	Sync time stamp with external clock
> @@ -64,7 +64,7 @@ void *ring_buffer_event_data(struct ring_buffer_event *event);
>   * ring_buffer_event_time_delta - return the delta timestamp of the event
>   * @event: the event to get the delta timestamp of
>   *
> - * The delta timestamp is the 27 bit timestamp since the last event.
> + * The delta timestamp is the 26 bit timestamp since the last event.
>   */
>  static inline unsigned
>  ring_buffer_event_time_delta(struct ring_buffer_event *event)
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index e773c57..33bdde2 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -183,7 +183,7 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
>  
>  #define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
>  #define RB_ALIGNMENT		4U
> -#define RB_MAX_SMALL_DATA	28
> +#define RB_MAX_SMALL_DATA	60
>  
>  enum {
>  	RB_LEN_TIME_EXTEND = 8,
> @@ -285,7 +285,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_event_data);
>  #define for_each_buffer_cpu(buffer, cpu)		\
>  	for_each_cpu(cpu, buffer->cpumask)
>  
> -#define TS_SHIFT	27
> +#define TS_SHIFT	26
>  #define TS_MASK		((1ULL << TS_SHIFT) - 1)
>  #define TS_DELTA_TEST	(~TS_MASK)
>  
> @@ -330,7 +330,7 @@ static void free_buffer_page(struct buffer_page *bpage)
>  }
>  
>  /*
> - * We need to fit the time_stamp delta into 27 bits.
> + * We need to fit the time_stamp delta into 26 bits.
>   */
>  static inline int test_time_stamp(u64 delta)
>  {
> @@ -1299,7 +1299,7 @@ rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
>  	static int once;
>  	int ret;
>  
> -	if (unlikely(*delta > (1ULL << 59) && !once++)) {
> +	if (unlikely(*delta > (1ULL << 58) && !once++)) {
>  		printk(KERN_WARNING "Delta way too big! %llu"
>  		       " ts=%llu write stamp = %llu\n",
>  		       (unsigned long long)*delta,
> 
> 

Re: [PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

[Lai Jiangshan]

Steven Rostedt wrote:
> On Mon, 2009-04-13 at 11:00 +0800, Lai Jiangshan wrote:
>> When I am writing userspace tools for ftrace, I found
>> RB_MAX_SMALL_DATA is too small, some events waste an 'u32'
>> to save the actually length.
> 
> Although I like the idea, I want to look at something else.
> 
> 2^27 is: 134,217,728
> 2^26 is: 67,108,864
> 
> That is the count in nanoseconds. Thus we go from 134 millisecs to 67
> millisecs before we must add an extended counter.
> 
> I guess that is not an issue, since 67ms is still quite big. For sparse
> tracing, it could add more extended counters where none were needed. But
> this I doubt this is an issue.

67ms < 0.1sec, It sounds not very good.

> 
>> This fix will break previous userspace tools,
>> so complaints are also welcome.
> 
> Unfortunately, this changes the API to userspace. For those parsers that
> do this in binary. I think the answer is, before we add this, we export
> the format of the ring buffer headers just like we do for other formats.
> This way, a user tool can default to the old way if the format file does
> not exist, and can know the current format with the file.
> 
> I'll work on adding that format file sometime this week.
>

I think ftrace is still in develop-circle, changing its API to userspace
is sometimes OK. Will you agreed this fix after you add that format file?
It saves about 0%-12%(depends on tracer) memory.

How about this method:

{u32 type_len:5, time_delta:27;};

time_delta is still 27bits, but RB_MAX_SMALL_DATA is increased to 112,
it is larger than 60 in my patch.

type_len  actual type                actual len
0         RINGBUF_TYPE_DATA,         array[0]
1 ~ 28    RINGBUF_TYPE_DATA          4*1 ~ 4*28
29        RINGBUF_TYPE_TIME_STAMP    
30        RINGBUF_TYPE_TIME_EXTEND
31        RINGBUF_TYPE_PADDING       array[0] if it's not the last event
                                     in the buffer_page(discarded event)
If you like this method, I will implement it.

Lai.

Re: [PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

[Ingo Molnar]

* Lai Jiangshan <laijs@cn.fujitsu.com> wrote:

> Steven Rostedt wrote:
> > On Mon, 2009-04-13 at 11:00 +0800, Lai Jiangshan wrote:
> >> When I am writing userspace tools for ftrace, I found
> >> RB_MAX_SMALL_DATA is too small, some events waste an 'u32'
> >> to save the actually length.
> > 
> > Although I like the idea, I want to look at something else.
> > 
> > 2^27 is: 134,217,728
> > 2^26 is: 67,108,864
> > 
> > That is the count in nanoseconds. Thus we go from 134 millisecs to 67
> > millisecs before we must add an extended counter.
> > 
> > I guess that is not an issue, since 67ms is still quite big. For sparse
> > tracing, it could add more extended counters where none were needed. But
> > this I doubt this is an issue.
> 
> 67ms < 0.1sec, It sounds not very good.
> 
> > 
> >> This fix will break previous userspace tools,
> >> so complaints are also welcome.
> > 
> > Unfortunately, this changes the API to userspace. For those parsers that
> > do this in binary. I think the answer is, before we add this, we export
> > the format of the ring buffer headers just like we do for other formats.
> > This way, a user tool can default to the old way if the format file does
> > not exist, and can know the current format with the file.
> > 
> > I'll work on adding that format file sometime this week.
> >
> 
> I think ftrace is still in develop-circle, changing its API to 
> userspace is sometimes OK. Will you agreed this fix after you add 
> that format file? It saves about 0%-12%(depends on tracer) memory.

Yes, /debug APIs can be changed indeed.

And compressing tracer memory consumption is a high priority design 
target: lower memory consumption doesnt just mean less RAM footprint 
and less disk footprint, it also means less CPU cache footprint, 
less intrusive tracing, faster tracing, etc. etc.

So compression is a very important goal - and we only want to stop 
doing it when the direct CPU overhead or the compression complexity 
it introduces offsets the size win. In this particular case we are 
still far from that cutoff point IMHO.

	Ingo

Re: [PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

[Steven Rostedt]

On Wed, 2009-04-15 at 17:14 +0800, Lai Jiangshan wrote:

> 
> How about this method:
> 
> {u32 type_len:5, time_delta:27;};
> 
> time_delta is still 27bits, but RB_MAX_SMALL_DATA is increased to 112,
> it is larger than 60 in my patch.
> 
> type_len  actual type                actual len
> 0         RINGBUF_TYPE_DATA,         array[0]
> 1 ~ 28    RINGBUF_TYPE_DATA          4*1 ~ 4*28
> 29        RINGBUF_TYPE_TIME_STAMP    
> 30        RINGBUF_TYPE_TIME_EXTEND
> 31        RINGBUF_TYPE_PADDING       array[0] if it's not the last event
>                                      in the buffer_page(discarded event)
> If you like this method, I will implement it.

I like the idea a lot. The only issue I have with it is that these types
are used a lot in switch statements, and in fast paths.

But the compression may be a better win.

We could do this in the switches.

	switch (event->type_len) {
	case RINGBUF_TYPE_TIME_STAMP:
		/**/
		break;
	case RINGBUF_TYPE_TIME_EXTEND:
		/**/
		break;
	case RINGBUF_TYPE_PADDING:
		/**/
		break;
	default: /* RINGBUF_TYPE_DATA */

	}

But before any of this goes in. I would like to export the interface.
Yes it is suppose to be OK to be able to change the interface, but the
binary output made it into 30. I doubt this change will make it before
31. If that's the case. We must have the format listed. 30 is expected
to be used by many distros. There's already tools using ftrace. If we
make a change that can not be caught, then it will break many tools.

We could ask Linus to pull this into 30 because it is a API change.

-- Steve

Re: [PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

[Ingo Molnar]

* Steven Rostedt <srostedt@redhat.com> wrote:

> 
> On Wed, 2009-04-15 at 17:14 +0800, Lai Jiangshan wrote:
> 
> > 
> > How about this method:
> > 
> > {u32 type_len:5, time_delta:27;};
> > 
> > time_delta is still 27bits, but RB_MAX_SMALL_DATA is increased to 112,
> > it is larger than 60 in my patch.
> > 
> > type_len  actual type                actual len
> > 0         RINGBUF_TYPE_DATA,         array[0]
> > 1 ~ 28    RINGBUF_TYPE_DATA          4*1 ~ 4*28
> > 29        RINGBUF_TYPE_TIME_STAMP    
> > 30        RINGBUF_TYPE_TIME_EXTEND
> > 31        RINGBUF_TYPE_PADDING       array[0] if it's not the last event
> >                                      in the buffer_page(discarded event)
> > If you like this method, I will implement it.
> 
> I like the idea a lot. The only issue I have with it is that these types
> are used a lot in switch statements, and in fast paths.
> 
> But the compression may be a better win.
> 
> We could do this in the switches.
> 
> 	switch (event->type_len) {
> 	case RINGBUF_TYPE_TIME_STAMP:
> 		/**/
> 		break;
> 	case RINGBUF_TYPE_TIME_EXTEND:
> 		/**/
> 		break;
> 	case RINGBUF_TYPE_PADDING:
> 		/**/
> 		break;
> 	default: /* RINGBUF_TYPE_DATA */
> 
> 	}
> 
> But before any of this goes in. I would like to export the 
> interface. Yes it is suppose to be OK to be able to change the 
> interface, but the binary output made it into 30. I doubt this 
> change will make it before 31. If that's the case. We must have 
> the format listed. 30 is expected to be used by many distros. 
> There's already tools using ftrace. If we make a change that can 
> not be caught, then it will break many tools.

Yeah - format specifications are always good. They weaken ABI 
bindings and allow more flexibility both on the tool and the kernel 
side.

> We could ask Linus to pull this into 30 because it is a API 
> change.

Apps could assume if the format file is not there it's the .30 
format.

	Ingo

Re: [PATCH] ring_buffer: enlarge RB_MAX_SMALL_DATA

[Steven Rostedt]

On Wed, 2009-04-15 at 16:12 +0200, Ingo Molnar wrote:
> * Steven Rostedt <srostedt@redhat.com> wrote:

> Yeah - format specifications are always good. They weaken ABI 
> bindings and allow more flexibility both on the tool and the kernel 
> side.
> 
> > We could ask Linus to pull this into 30 because it is a API 
> > change.
> 
> Apps could assume if the format file is not there it's the .30 
> format.

My fear is that they are written before the change, and will not know
about a format file existing. Then those apps will break on 31.

But this is still new, and the only user I know of at the moment is the
University student doing the ftrace GUI. I'll keep him informed.

Thanks,

-- Steve