rtla/timerlat: Add --dma-latency option

Add the --dma-latency to set /dev/cpu_dma_latency to the
specified value, this aims to avoid having exit from idle
states latencies that could be influencing the analysis.

Link: https://lkml.kernel.org/r/72ddb0d913459f13217086dadafad88a7c46dd28.1646247211.git.bristot@kernel.org

Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 26 insertions, 2 deletions

diff --git a/tools/tracing/rtla/src/timerlat_top.c b/tools/tracing/rtla/src/timerlat_top.c
index bf2a50350e61..53f4cdfd395e 100644
--- a/tools/tracing/rtla/src/timerlat_top.c
+++ b/tools/tracing/rtla/src/timerlat_top.c
@@ -29,6 +29,7 @@ struct timerlat_top_params {
 	int			duration;
 	int			quiet;
 	int			set_sched;
+	int			dma_latency;
 	struct sched_attr	sched_param;
 	struct trace_events	*events;
 };
@@ -269,7 +270,7 @@ static void timerlat_top_usage(char *usage)
 		"",
 		"  usage: rtla timerlat [top] [-h] [-q] [-a us] [-d s] [-D] [-n] [-p us] [-i us] [-T us] [-s us] \\",
 		"	  [[-t[=file]] [-e sys[:event]] [--filter <filter>] [--trigger <trigger>] [-c cpu-list] \\",
-		"	  [-P priority]",
+		"	  [-P priority] [--dma-latency us]",
 		"",
 		"	  -h/--help: print this menu",
 		"	  -a/--auto: set automatic trace mode, stopping the session if argument in us latency is hit",
@@ -286,6 +287,7 @@ static void timerlat_top_usage(char *usage)
 		"	     --trigger <command>: enable a trace event trigger to the previous -e event",
 		"	  -n/--nano: display data in nanoseconds",
 		"	  -q/--quiet print only a summary at the end",
+		"	     --dma-latency us: set /dev/cpu_dma_latency latency <us> to reduce exit from idle latency",
 		"	  -P/--priority o:prio|r:prio|f:prio|d:runtime:period : set scheduling parameters",
 		"		o:prio - use SCHED_OTHER with prio",
 		"		r:prio - use SCHED_RR with prio",
@@ -322,6 +324,9 @@ static struct timerlat_top_params
 	if (!params)
 		exit(1);
 
+	/* disabled by default */
+	params->dma_latency = -1;
+
 	/* display data in microseconds */
 	params->output_divisor = 1000;
 
@@ -343,13 +348,14 @@ static struct timerlat_top_params
 			{"trace",		optional_argument,	0, 't'},
 			{"trigger",		required_argument,	0, '0'},
 			{"filter",		required_argument,	0, '1'},
+			{"dma-latency",		required_argument,	0, '2'},
 			{0, 0, 0, 0}
 		};
 
 		/* getopt_long stores the option index here. */
 		int option_index = 0;
 
-		c = getopt_long(argc, argv, "a:c:d:De:hi:np:P:qs:t::T:0:1:",
+		c = getopt_long(argc, argv, "a:c:d:De:hi:np:P:qs:t::T:0:1:2:",
 				 long_options, &option_index);
 
 		/* detect the end of the options. */
@@ -454,6 +460,13 @@ static struct timerlat_top_params
 				timerlat_top_usage("--filter requires a previous -e\n");
 			}
 			break;
+		case '2': /* dma-latency */
+			params->dma_latency = get_llong_from_str(optarg);
+			if (params->dma_latency < 0 || params->dma_latency > 10000) {
+				err_msg("--dma-latency needs to be >= 0 and < 10000");
+				exit(EXIT_FAILURE);
+			}
+			break;
 		default:
 			timerlat_top_usage("Invalid option");
 		}
@@ -582,6 +595,7 @@ int timerlat_top_main(int argc, char *argv[])
 	struct osnoise_tool *record = NULL;
 	struct osnoise_tool *top = NULL;
 	struct trace_instance *trace;
+	int dma_latency_fd = -1;
 	int return_value = 1;
 	int retval;
 
@@ -617,6 +631,14 @@ int timerlat_top_main(int argc, char *argv[])
 		}
 	}
 
+	if (params->dma_latency >= 0) {
+		dma_latency_fd = set_cpu_dma_latency(params->dma_latency);
+		if (dma_latency_fd < 0) {
+			err_msg("Could not set /dev/cpu_dma_latency.\n");
+			goto out_top;
+		}
+	}
+
 	trace_instance_start(trace);
 
 	if (params->trace_output) {
@@ -673,6 +695,8 @@ int timerlat_top_main(int argc, char *argv[])
 	}
 
 out_top:
+	if (dma_latency_fd >= 0)
+		close(dma_latency_fd);
 	trace_events_destroy(&record->trace, params->events);
 	params->events = NULL;
 	timerlat_free_top(top->data);