From 2c1ea60b195da6c4661ec5e4d61f68b8b34e113b Mon Sep 17 00:00:00 2001 From: Tom Zanussi Date: Mon, 15 Jan 2018 20:51:41 -0600 Subject: [PATCH] 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 Signed-off-by: Steven Rostedt (VMware) --- Documentation/trace/ftrace.txt | 24 +++++++++++++++++ kernel/trace/trace.c | 47 ++++++++++++++++++++++++++++++++++ 2 files changed, 71 insertions(+) diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt index d4601df6e72e..54213e5c23f6 100644 --- a/Documentation/trace/ftrace.txt +++ b/Documentation/trace/ftrace.txt @@ -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. diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index cba003f0362e..988d94a05e81 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -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) -- 2.30.2