[v4,10/46] tools/lib/traceevent: Man page for tep_is_latency_format() and tep_set_latency_format()

Commit Message

Tzvetomir Stoyanov March 8, 2019, 1:36 p.m. UTC

Create man pages for tep_is_latency_format() and tep_set_latency_format()
as part of the libtraceevent APIs.

Signed-off-by: Tzvetomir Stoyanov <[e-mail]>
---
 .../libtraceevent-latency_format.txt          | 140 ++++++++++++++++++
 1 file changed, 140 insertions(+)
 create mode 100644 tools/lib/traceevent/Documentation/libtraceevent-latency_format.txt

Comments

Steven Rostedt March 13, 2019, 4:28 p.m. UTC | #1

On Fri,  8 Mar 2019 15:36:18 +0200
Tzvetomir Stoyanov <[e-mail]> wrote:

> +  <idle>-0       0d.h1. 106467.859747: function:             ktime_get <-- tick_check_idle
> +--
> +The 0d.h1. denotes this information. The first character is never a pass:['.']
> +and represents what CPU the trace was recorded on (CPU 0). The pass:['d'] denotes
> +that interrupts were disabled. The pass:['h'] means that this was called inside
> +an interrupt handler. The pass:['1'] is the preemption disabled (preempt_count)
> +was set to one.  The two pass:['.']s are "need_resched" flag and kernel lock

There is no kernel lock counter.

Should delete that last '.' in the example.

-- Steve

> +counter. If the "need_resched" flag is set, then that character would be a pass:['N'].
> +See 'LATENCY FORMAT' section.

Patch

diff --git a/tools/lib/traceevent/Documentation/libtraceevent-latency_format.txt b/tools/lib/traceevent/Documentation/libtraceevent-latency_format.txt
new file mode 100644
index 000000000000..ea82cbda7b7c
--- /dev/null
+++ b/tools/lib/traceevent/Documentation/libtraceevent-latency_format.txt
@@ -0,0 +1,140 @@ 
+libtraceevent(3)
+================
+
+NAME
+----
+tep_set_latency_format,tep_is_latency_format - Get / set "latency output" format.
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <event-parse.h>*
+
+void *tep_set_latency_format*(struct tep_handle pass:[*]_tep_, int _lat_);
+int *tep_is_latency_format*(struct tep_handle pass:[*]_tep_);
+
+--
+
+DESCRIPTION
+-----------
+"Latency output" format prints information about interrupts being disabled,
+soft irq being disabled, the "need_resched" flag being set and preempt count.
+This information is recorded with every event, but by default is not printed.
+
+The _tep_set_latency_format()_ function enables the "latency output" printing.
+The _tep_ argument is trace event parser context. The _lat_ argument can be zero,
+for "latency output" disabled, or non zero for "latency output" enabled.
+Information is displayed with 6 characters. When a field is zero, or N/A, a pass:['.']
+is printed. Example:
+[verse]
+--
+  <idle>-0       0d.h1. 106467.859747: function:             ktime_get <-- tick_check_idle
+--
+The 0d.h1. denotes this information. The first character is never a pass:['.']
+and represents what CPU the trace was recorded on (CPU 0). The pass:['d'] denotes
+that interrupts were disabled. The pass:['h'] means that this was called inside
+an interrupt handler. The pass:['1'] is the preemption disabled (preempt_count)
+was set to one.  The two pass:['.']s are "need_resched" flag and kernel lock
+counter. If the "need_resched" flag is set, then that character would be a pass:['N'].
+See 'LATENCY FORMAT' section.
+
+The _tep_is_latency_format()_ function returns if "latency output" is enabled.
+
+This "Latency output" setting affects output of _tep_print_event_task()_
+and _tep_print_event_time()_ APIs.
+
+LATENCY FORMAT
+--------------
+The latency format displays 5 or more fields:
+[verse]
+--
+ CPU #, interrupt state, scheduling state, current context, and preemption count.
+
+ Field 1 is the CPU number (starting with zero).
+
+ Field 2 is the interrupt enabled state:
+   d : Interrupts are disabled
+   . : Interrupts are enabled
+   X : The architecture does not support this information
+
+ Field 3 is the "need resched" state.
+   N : The task is set to call the scheduler when possible, as another
+       higher priority task may need to be scheduled in.
+   . : The task is not set to call the scheduler.
+
+ Field 4 is the context state.
+   . : Normal context
+   s : Soft interrupt context
+   h : Hard interrupt context
+   H : Hard interrupt context which triggered during soft interrupt context.
+   z : NMI context
+   Z : NMI context which triggered during hard interrupt context
+
+ Field 5 is the preemption count.
+   . : The preempt count is zero.
+
+   On preemptible kernels (where the task can be scheduled out in
+   arbitrary locations while in kernel context), The preempt count,
+   when non zero, will prevent the kernel from scheduling out the
+   current task. The preempt count number is displayed when it is not
+   zero.
+--
+Depending on the kernel, it may show other fields (lock depth,
+or migration disabled, which are unique to specialized kernels).
+
+RETURN VALUE
+------------
+
+The _tep_is_latency_format()_ function returns non zero if "latency output"
+is enabled, or zero if it is disabled.
+
+EXAMPLE
+-------
+[source,c]
+--
+#include <event-parse.h>
+...
+struct tep_handle *tep = tep_alloc();
+...
+	tep_set_latency_format(tep, 1);
+...
+	if (tep_is_latency_format(tep)) {
+		/* latency output format is enabled */
+	} else {
+		/* latency output format is disabled */
+	}
+--
+
+FILES
+-----
+[verse]
+--
+*event-parse.h*
+	Header file to include in order to have access to the library APIs.
+*-ltraceevent*
+	Linker switch to add when building a program that uses the library.
+--
+
+SEE ALSO
+--------
+_libtraceevent(3)_, _trace-cmd(1)_, tep_print_event_task(3), tep_print_event_time(3)
+
+AUTHOR
+------
+[verse]
+--
+*Steven Rostedt* <[e-mail]>, author of *libtraceevent*.
+*Tzvetomir Stoyanov* <[e-mail]>, author of this man page.
+--
+REPORTING BUGS
+--------------
+Report bugs to  <[e-mail]>
+
+LICENSE
+-------
+libtraceevent is Free Software licensed under the GNU LGPL 2.1
+
+RESOURCES
+---------
+https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git