[RFC][PATCH 0/2] tracing: Better snapshot handling and documentation

[RFC][PATCH 0/2] tracing: Better snapshot handling and documentation

[Steven Rostedt]

Hiraku,

Here's the patches that I updated to the snapshot feature.
Can you add your Acked-by. I want this to get into 3.9 as the current
method shouldn't become an ABI yet.

Thanks!

-- Steve


Steven Rostedt (Red Hat) (2):
      tracing: Add help of snapshot feature when snapshot is empty
      tracing: Do not return EINVAL in snapshot when not allocated

----
 kernel/trace/trace.c |   27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

[RFC][PATCH 1/2] tracing: Add help of snapshot feature when snapshot is empty

[Steven Rostedt]

[-- Attachment #1: 0001-tracing-Add-help-of-snapshot-feature-when-snapshot-i.patch --]
[-- Type: text/plain, Size: 3424 bytes --]

From: "Steven Rostedt (Red Hat)" <srostedt@redhat.com>

When cat'ing the snapshot file, instead of showing an empty trace
header like the trace file does, show how to use the snapshot
feature.

Also, this is a good place to show if the snapshot has been allocated
or not. Users may want to "pre allocate" the snapshot to have a fast
"swap" of the current buffer. Otherwise, a swap would be slow and might
fail as it would need to allocate the snapshot buffer, and that might
fail under tight memory constraints.

Here's what it looked like before:

 # tracer: nop
 #
 # entries-in-buffer/entries-written: 0/0   #P:4
 #
 #                              _-----=> irqs-off
 #                             / _----=> need-resched
 #                            | / _---=> hardirq/softirq
 #                            || / _--=> preempt-depth
 #                            ||| /     delay
 #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
 #              | |       |   ||||       |         |

Here's what it looks like now:

 # tracer: nop
 #
 #
 # * Snapshot is freed *
 #
 # Snapshot commands:
 # echo 0 > snapshot : Clears and frees snapshot buffer
 # echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.
 #                      Takes a snapshot of the main buffer.
 # echo 2 > snapshot : Clears snapshot buffer (but does not allocate)
 #                      (Doesn't have to be '2' works with any number that
 #                       is not a '0' or '1')

Cc: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace.c |   25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c2e2c23..9e3120b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -2400,6 +2400,27 @@ static void test_ftrace_alive(struct seq_file *m)
 	seq_printf(m, "#          MAY BE MISSING FUNCTION EVENTS\n");
 }
 
+#ifdef CONFIG_TRACER_MAX_TRACE
+static void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter)
+{
+	if (iter->trace->allocated_snapshot)
+		seq_printf(m, "#\n# * Snapshot is allocated *\n#\n");
+	else
+		seq_printf(m, "#\n# * Snapshot is freed *\n#\n");
+
+	seq_printf(m, "# Snapshot commands:\n");
+	seq_printf(m, "# echo 0 > snapshot : Clears and frees snapshot buffer\n");
+	seq_printf(m, "# echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.\n");
+	seq_printf(m, "#                      Takes a snapshot of the main buffer.\n");
+	seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does not allocate)\n");
+	seq_printf(m, "#                      (Doesn't have to be '2' works with any number that\n");
+	seq_printf(m, "#                       is not a '0' or '1')\n");
+}
+#else
+/* Should never be called */
+static inline void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter) { }
+#endif
+
 static int s_show(struct seq_file *m, void *v)
 {
 	struct trace_iterator *iter = v;
@@ -2411,7 +2432,9 @@ static int s_show(struct seq_file *m, void *v)
 			seq_puts(m, "#\n");
 			test_ftrace_alive(m);
 		}
-		if (iter->trace && iter->trace->print_header)
+		if (iter->snapshot && trace_empty(iter))
+			print_snapshot_help(m, iter);
+		else if (iter->trace && iter->trace->print_header)
 			iter->trace->print_header(m);
 		else
 			trace_default_header(m);
-- 
1.7.10.4

[RFC][PATCH 2/2] tracing: Do not return EINVAL in snapshot when not allocated

[Steven Rostedt]

[-- Attachment #1: 0002-tracing-Do-not-return-EINVAL-in-snapshot-when-not-al.patch --]
[-- Type: text/plain, Size: 1250 bytes --]

From: "Steven Rostedt (Red Hat)" <srostedt@redhat.com>

To use the tracing snapshot feature, writing a '1' into the snapshot
file causes the snapshot buffer to be allocated if it has not already
been allocated and dose a 'swap' with the main buffer, so that the
snapshot now contains what was in the main buffer, and the main buffer
now writes to what was the snapshot buffer.

To free the snapshot buffer, a '0' is written into the snapshot file.

To clear the snapshot buffer, any number but a '0' or '1' is written
into the snapshot file. But if the file is not allocated it returns
-EINVAL error code. This is rather pointless. It is better just to
do nothing and return success.

Cc: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace.c |    2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 9e3120b..1f835a8 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4167,8 +4167,6 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
 	default:
 		if (current_trace->allocated_snapshot)
 			tracing_reset_online_cpus(&max_tr);
-		else
-			ret = -EINVAL;
 		break;
 	}
 
-- 
1.7.10.4

Re: [RFC][PATCH 1/2] tracing: Add help of snapshot feature when snapshot is empty

[Hiraku Toyooka]

(03/06/2013 10:49 PM), Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)"<srostedt@redhat.com>
> 
> When cat'ing the snapshot file, instead of showing an empty trace
> header like the trace file does, show how to use the snapshot
> feature.
> 
> Also, this is a good place to show if the snapshot has been allocated
> or not. Users may want to "pre allocate" the snapshot to have a fast
> "swap" of the current buffer. Otherwise, a swap would be slow and might
> fail as it would need to allocate the snapshot buffer, and that might
> fail under tight memory constraints.
> 
> Here's what it looked like before:
> 
>   # tracer: nop
>   #
>   # entries-in-buffer/entries-written: 0/0   #P:4
>   #
>   #                              _-----=> irqs-off
>   #                             / _----=> need-resched
>   #                            | / _---=> hardirq/softirq
>   #                            || / _--=> preempt-depth
>   #                            ||| /     delay
>   #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
>   #              | |       |   ||||       |         |
> 
> Here's what it looks like now:
> 
>   # tracer: nop
>   #
>   #
>   # * Snapshot is freed *
>   #
>   # Snapshot commands:
>   # echo 0 > snapshot : Clears and frees snapshot buffer
>   # echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.
>   #                      Takes a snapshot of the main buffer.
>   # echo 2 > snapshot : Clears snapshot buffer (but does not allocate)
>   #                      (Doesn't have to be '2' works with any number that
>   #                       is not a '0' or '1')
> 
> Cc: Hiraku Toyooka<hiraku.toyooka.gu@hitachi.com>
> Signed-off-by: Steven Rostedt<rostedt@goodmis.org>
> ---

Acked-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>

>   kernel/trace/trace.c |   25 ++++++++++++++++++++++++-
>   1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index c2e2c23..9e3120b 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2400,6 +2400,27 @@ static void test_ftrace_alive(struct seq_file *m)
>   	seq_printf(m, "#          MAY BE MISSING FUNCTION EVENTS\n");
>   }
>   
> +#ifdef CONFIG_TRACER_MAX_TRACE
> +static void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter)
> +{
> +	if (iter->trace->allocated_snapshot)
> +		seq_printf(m, "#\n# * Snapshot is allocated *\n#\n");
> +	else
> +		seq_printf(m, "#\n# * Snapshot is freed *\n#\n");
> +
> +	seq_printf(m, "# Snapshot commands:\n");
> +	seq_printf(m, "# echo 0 > snapshot : Clears and frees snapshot buffer\n");
> +	seq_printf(m, "# echo 1 > snapshot : Allocates snapshot buffer, if not already allocated.\n");
> +	seq_printf(m, "#                      Takes a snapshot of the main buffer.\n");
> +	seq_printf(m, "# echo 2 > snapshot : Clears snapshot buffer (but does not allocate)\n");
> +	seq_printf(m, "#                      (Doesn't have to be '2' works with any number that\n");
> +	seq_printf(m, "#                       is not a '0' or '1')\n");
> +}
> +#else
> +/* Should never be called */
> +static inline void print_snapshot_help(struct seq_file *m, struct trace_iterator *iter) { }
> +#endif
> +
>   static int s_show(struct seq_file *m, void *v)
>   {
>   	struct trace_iterator *iter = v;
> @@ -2411,7 +2432,9 @@ static int s_show(struct seq_file *m, void *v)
>   			seq_puts(m, "#\n");
>   			test_ftrace_alive(m);
>   		}
> -		if (iter->trace && iter->trace->print_header)
> +		if (iter->snapshot && trace_empty(iter))
> +			print_snapshot_help(m, iter);
> +		else if (iter->trace && iter->trace->print_header)
>   			iter->trace->print_header(m);
>   		else
>   			trace_default_header(m);
> -- 1.7.10.4 .
> 

Re: [RFC][PATCH 2/2] tracing: Do not return EINVAL in snapshot when not allocated

[Hiraku Toyooka]

(03/06/2013 10:49 PM), Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)"<srostedt@redhat.com>
> 
> To use the tracing snapshot feature, writing a '1' into the snapshot
> file causes the snapshot buffer to be allocated if it has not already
> been allocated and dose a 'swap' with the main buffer, so that the
> snapshot now contains what was in the main buffer, and the main buffer
> now writes to what was the snapshot buffer.
> 
> To free the snapshot buffer, a '0' is written into the snapshot file.
> 
> To clear the snapshot buffer, any number but a '0' or '1' is written
> into the snapshot file. But if the file is not allocated it returns
> -EINVAL error code. This is rather pointless. It is better just to
> do nothing and return success.
> 
> Cc: Hiraku Toyooka<hiraku.toyooka.gu@hitachi.com>
> Signed-off-by: Steven Rostedt<rostedt@goodmis.org>
> ---

Acked-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>

>   kernel/trace/trace.c |    2 --
>   1 file changed, 2 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 9e3120b..1f835a8 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -4167,8 +4167,6 @@ tracing_snapshot_write(struct file *filp, const char __user *ubuf, size_t cnt,
>   	default:
>   		if (current_trace->allocated_snapshot)
>   			tracing_reset_online_cpus(&max_tr);
> -		else
> -			ret = -EINVAL;
>   		break;
>   	}
>   
> -- 1.7.10.4 .
>