[PATCH V3 14/15] rtla/timerlat: Add --dma-latency option

From: Daniel Bristot de Oliveira
Date: Wed Mar 02 2022 - 14:04:44 EST

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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.

Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
---
.../tools/rtla/common_timerlat_options.rst | 5 +++
tools/tracing/rtla/src/timerlat_hist.c | 28 ++++++++++++++--
tools/tracing/rtla/src/timerlat_top.c | 28 ++++++++++++++--
tools/tracing/rtla/src/utils.c | 33 +++++++++++++++++++
tools/tracing/rtla/src/utils.h | 1 +
5 files changed, 91 insertions(+), 4 deletions(-)

diff --git a/Documentation/tools/rtla/common_timerlat_options.rst b/Documentation/tools/rtla/common_timerlat_options.rst
index 14a24a121f5d..bacdea6de7a3 100644
--- a/Documentation/tools/rtla/common_timerlat_options.rst
+++ b/Documentation/tools/rtla/common_timerlat_options.rst
@@ -21,3 +21,8 @@

Save the stack trace at the *IRQ* if a *Thread* latency is higher than the
argument in us.
+
+**--dma-latency** *us*
+ Set the /dev/cpu_dma_latency to *us*, aiming to bound exit from idle latencies.
+ *cyclictest* sets this value to *0* by default, use **--dma-latency** *0* to have
+ similar results.
diff --git a/tools/tracing/rtla/src/timerlat_hist.c b/tools/tracing/rtla/src/timerlat_hist.c
index 17188ccb6e8b..0f6ce80a198a 100644
--- a/tools/tracing/rtla/src/timerlat_hist.c
+++ b/tools/tracing/rtla/src/timerlat_hist.c
@@ -28,6 +28,7 @@ struct timerlat_hist_params {
int output_divisor;
int duration;
int set_sched;
+ int dma_latency;
struct sched_attr sched_param;
struct trace_events *events;

@@ -432,7 +433,7 @@ static void timerlat_hist_usage(char *usage)
" usage: [rtla] timerlat hist [-h] [-q] [-d s] [-D] [-n] [-a us] [-p us] [-i us] [-T us] [-s us] \\",
" [-t[=file]] [-e sys[:event]] [--filter <filter>] [--trigger <trigger>] [-c cpu-list] \\",
" [-P priority] [-E N] [-b N] [--no-irq] [--no-thread] [--no-header] [--no-summary] \\",
- " [--no-index] [--with-zeros]",
+ " [--no-index] [--with-zeros] [--dma-latency us]",
"",
" -h/--help: print this menu",
" -a/--auto: set automatic trace mode, stopping the session if argument in us latency is hit",
@@ -456,6 +457,7 @@ static void timerlat_hist_usage(char *usage)
" --no-summary: do not print summary",
" --no-index: do not print index",
" --with-zeros: print zero only entries",
+ " --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",
@@ -492,6 +494,9 @@ static struct timerlat_hist_params
if (!params)
exit(1);

+ /* disabled by default */
+ params->dma_latency = -1;
+
/* display data in microseconds */
params->output_divisor = 1000;
params->bucket_size = 1;
@@ -522,13 +527,14 @@ static struct timerlat_hist_params
{"with-zeros", no_argument, 0, '5'},
{"trigger", required_argument, 0, '6'},
{"filter", required_argument, 0, '7'},
+ {"dma-latency", required_argument, 0, '8'},
{0, 0, 0, 0}
};

/* getopt_long stores the option index here. */
int option_index = 0;

- c = getopt_long(argc, argv, "a:c:b:d:e:E:Dhi:np:P:s:t::T:0123456:7:",
+ c = getopt_long(argc, argv, "a:c:b:d:e:E:Dhi:np:P:s:t::T:0123456:7:8:",
long_options, &option_index);

/* detect the end of the options. */
@@ -659,6 +665,13 @@ static struct timerlat_hist_params
timerlat_hist_usage("--filter requires a previous -e\n");
}
break;
+ case '8':
+ 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_hist_usage("Invalid option");
}
@@ -791,6 +804,7 @@ int timerlat_hist_main(int argc, char *argv[])
struct osnoise_tool *record = NULL;
struct osnoise_tool *tool = NULL;
struct trace_instance *trace;
+ int dma_latency_fd = -1;
int return_value = 1;
int retval;

@@ -826,6 +840,14 @@ int timerlat_hist_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_hist;
+ }
+ }
+
trace_instance_start(trace);

if (params->trace_output) {
@@ -878,6 +900,8 @@ int timerlat_hist_main(int argc, char *argv[])
}

out_hist:
+ if (dma_latency_fd >= 0)
+ close(dma_latency_fd);
trace_events_destroy(&record->trace, params->events);
params->events = NULL;
timerlat_free_histogram(tool->data);
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);
diff --git a/tools/tracing/rtla/src/utils.c b/tools/tracing/rtla/src/utils.c
index ffaf8ec84001..da2b590edaed 100644
--- a/tools/tracing/rtla/src/utils.c
+++ b/tools/tracing/rtla/src/utils.c
@@ -10,6 +10,7 @@
#include <unistd.h>
#include <ctype.h>
#include <errno.h>
+#include <fcntl.h>
#include <sched.h>
#include <stdio.h>

@@ -431,3 +432,35 @@ int parse_prio(char *arg, struct sched_attr *sched_param)
}
return 0;
}
+
+/*
+ * set_cpu_dma_latency - set the /dev/cpu_dma_latecy
+ *
+ * This is used to reduce the exit from idle latency. The value
+ * will be reset once the file descriptor of /dev/cpu_dma_latecy
+ * is closed.
+ *
+ * Return: the /dev/cpu_dma_latecy file descriptor
+ */
+int set_cpu_dma_latency(int32_t latency)
+{
+ int retval;
+ int fd;
+
+ fd = open("/dev/cpu_dma_latency", O_RDWR);
+ if (fd < 0) {
+ err_msg("Error opening /dev/cpu_dma_latency\n");
+ return -1;
+ }
+
+ retval = write(fd, &latency, 4);
+ if (retval < 1) {
+ err_msg("Error setting /dev/cpu_dma_latency\n");
+ close(fd);
+ return -1;
+ }
+
+ debug_msg("Set /dev/cpu_dma_latency to %d\n", latency);
+
+ return fd;
+}
diff --git a/tools/tracing/rtla/src/utils.h b/tools/tracing/rtla/src/utils.h
index 9aa962319ca2..fa08e374870a 100644
--- a/tools/tracing/rtla/src/utils.h
+++ b/tools/tracing/rtla/src/utils.h
@@ -54,3 +54,4 @@ struct sched_attr {

int parse_prio(char *arg, struct sched_attr *sched_param);
int set_comm_sched_attr(const char *comm, struct sched_attr *attr);
+int set_cpu_dma_latency(int32_t latency);
--
2.34.1

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