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tracing: Add timestamp_mode trace file 

Add a new option flag indicating whether or not the ring buffer is in
'absolute timestamp' mode.

Currently this is only set/unset by hist triggers that make use of a
common_timestamp.  As such, there's no reason to make this writeable
for users - its purpose is only to allow users to determine
unequivocally whether or not the ring buffer is in that mode (although
absolute timestamps can coexist with the normal delta timestamps, when
the ring buffer is in absolute mode, timestamps written while absolute
mode is in effect take up more space in the buffer, and are not as
efficient).

Link: http://lkml.kernel.org/r/e8aa7b1cde1cf15014e66545d06ac6ef2ebba456.1516069914.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Tom Zanussi 2018-01-15 20:51:41 -06:00 committed by Steven Rostedt (VMware)
parent dc4e2801d4
commit 2c1ea60b19
2 changed files with 71 additions and 0 deletions
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24
Documentation/trace/ftrace.txt
View File

@ -539,6 +539,30 @@ of ftrace. Here is a list of some of the key files:
See events.txt for more information.
timestamp_mode:
Certain tracers may change the timestamp mode used when
logging trace events into the event buffer. Events with
different modes can coexist within a buffer but the mode in
effect when an event is logged determines which timestamp mode
is used for that event. The default timestamp mode is
'delta'.
Usual timestamp modes for tracing:
# cat timestamp_mode
[delta] absolute
The timestamp mode with the square brackets around it is the
one in effect.
delta: Default timestamp mode - timestamp is a delta against
a per-buffer timestamp.
absolute: The timestamp is a full timestamp, not a delta
against some other value. As such it takes up more
space and is less efficient.
hwlat_detector:
Directory for the Hardware Latency Detector.

47
kernel/trace/trace.c
View File

@ -4515,6 +4515,9 @@ static const char readme_msg[] =
#ifdef CONFIG_X86_64
" x86-tsc: TSC cycle counter\n"
#endif
"\n timestamp_mode\t-view the mode used to timestamp events\n"
" delta: Delta difference against a buffer-wide timestamp\n"
" absolute: Absolute (standalone) timestamp\n"
"\n trace_marker\t\t- Writes into this file writes into the kernel buffer\n"
"\n trace_marker_raw\t\t- Writes into this file writes binary data into the kernel buffer\n"
" tracing_cpumask\t- Limit which CPUs to trace\n"
@ -6282,6 +6285,40 @@ static int tracing_clock_open(struct inode *inode, struct file *file)
return ret;
}
static int tracing_time_stamp_mode_show(struct seq_file *m, void *v)
{
struct trace_array *tr = m->private;
mutex_lock(&trace_types_lock);
if (ring_buffer_time_stamp_abs(tr->trace_buffer.buffer))
seq_puts(m, "delta [absolute]\n");
else
seq_puts(m, "[delta] absolute\n");
mutex_unlock(&trace_types_lock);
return 0;
}
static int tracing_time_stamp_mode_open(struct inode *inode, struct file *file)
{
struct trace_array *tr = inode->i_private;
int ret;
if (tracing_disabled)
return -ENODEV;
if (trace_array_get(tr))
return -ENODEV;
ret = single_open(file, tracing_time_stamp_mode_show, inode->i_private);
if (ret < 0)
trace_array_put(tr);
return ret;
}
int tracing_set_time_stamp_abs(struct trace_array *tr, bool abs)
{
int ret = 0;
@ -6560,6 +6597,13 @@ static const struct file_operations trace_clock_fops = {
.write = tracing_clock_write,
};
static const struct file_operations trace_time_stamp_mode_fops = {
.open = tracing_time_stamp_mode_open,
.read = seq_read,
.llseek = seq_lseek,
.release = tracing_single_release_tr,
};
#ifdef CONFIG_TRACER_SNAPSHOT
static const struct file_operations snapshot_fops = {
.open = tracing_snapshot_open,
@ -7882,6 +7926,9 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
trace_create_file("tracing_on", 0644, d_tracer,
tr, &rb_simple_fops);
trace_create_file("timestamp_mode", 0444, d_tracer, tr,
&trace_time_stamp_mode_fops);
create_trace_options_dir(tr);
#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)