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>

diff --git a/Documentation/tools/rtla/common_timerlat_options.rst b/Documentation/tools/rtla/common_timerlat_options.rst
index 14a24a1..bacdea6 100644 (file)
--- 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 17188cc..0f6ce80 100644 (file)
--- 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 bf2a503..53f4cdf 100644 (file)
--- 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 ffaf8ec..da2b590 100644 (file)
--- 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 9aa9623..fa08e37 100644 (file)
--- 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);