rtla: Add --house-keeping option

To avoid having rtla interfering with the measurement threads, add an
option for the user to set the CPUs in which rtla should run. For
instance:

  # rtla timerlat top -H 0 -c 1-7

Will place rtla in the CPU 0, while running the measurement threads in
the CPU 1-7.

Link: https://lkml.kernel.org/r/6a6c78a579a96ba8b02ae67ee1e0ba2cb5e03c4a.1686066600.git.bristot@kernel.org

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

1 files changed, 25 insertions, 2 deletions

diff --git a/tools/tracing/rtla/src/timerlat_top.c b/tools/tracing/rtla/src/timerlat_top.c
index a19cbc2aa1f4..5395d1c5921e 100644
--- a/tools/tracing/rtla/src/timerlat_top.c
+++ b/tools/tracing/rtla/src/timerlat_top.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2021 Red Hat Inc, Daniel Bristot de Oliveira <bristot@kernel.org>
  */
 
+#define _GNU_SOURCE
 #include <getopt.h>
 #include <stdlib.h>
 #include <string.h>
@@ -11,6 +12,7 @@
 #include <stdio.h>
 #include <time.h>
 #include <errno.h>
+#include <sched.h>
 
 #include "utils.h"
 #include "osnoise.h"
@@ -37,6 +39,8 @@ struct timerlat_top_params {
 	int			aa_only;
 	int			dump_tasks;
 	int			cgroup;
+	int			hk_cpus;
+	cpu_set_t		hk_cpu_set;
 	struct sched_attr	sched_param;
 	struct trace_events	*events;
 };
@@ -286,7 +290,7 @@ static void timerlat_top_usage(char *usage)
 	static const char *const msg[] = {
 		"",
 		"  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] \\",
+		"	  [[-t[=file]] [-e sys[:event]] [--filter <filter>] [--trigger <trigger>] [-c cpu-list] [-H cpu-list]\\",
 		"	  [-P priority] [--dma-latency us] [--aa-only us] [-C[=cgroup_name]]",
 		"",
 		"	  -h/--help: print this menu",
@@ -297,6 +301,7 @@ static void timerlat_top_usage(char *usage)
 		"	  -T/--thread us: stop trace if the thread latency is higher than the argument in us",
 		"	  -s/--stack us: save the stack trace at the IRQ if a thread latency is higher than the argument in us",
 		"	  -c/--cpus cpus: run the tracer only on the given cpus",
+		"	  -H/--house-keeping cpus: run rtla control threads only on the given cpus",
 		"	  -C/--cgroup[=cgroup_name]: set cgroup, if no cgroup_name is passed, the rtla's cgroup will be inherited",
 		"	  -d/--duration time[m|h|d]: duration of the session in seconds",
 		"	  -D/--debug: print debug info",
@@ -360,6 +365,7 @@ static struct timerlat_top_params
 			{"duration",		required_argument,	0, 'd'},
 			{"event",		required_argument,	0, 'e'},
 			{"help",		no_argument,		0, 'h'},
+			{"house-keeping",	required_argument,	0, 'H'},
 			{"irq",			required_argument,	0, 'i'},
 			{"nano",		no_argument,		0, 'n'},
 			{"period",		required_argument,	0, 'p'},
@@ -380,7 +386,7 @@ static struct timerlat_top_params
 		/* getopt_long stores the option index here. */
 		int option_index = 0;
 
-		c = getopt_long(argc, argv, "a:c:C::d:De:hi:np:P:qs:t::T:0:1:2:345:",
+		c = getopt_long(argc, argv, "a:c:C::d:De:hH:i:np:P:qs:t::T:0:1:2:345:",
 				 long_options, &option_index);
 
 		/* detect the end of the options. */
@@ -454,6 +460,14 @@ static struct timerlat_top_params
 		case '?':
 			timerlat_top_usage(NULL);
 			break;
+		case 'H':
+			params->hk_cpus = 1;
+			retval = parse_cpu_set(optarg, &params->hk_cpu_set);
+			if (retval) {
+				err_msg("Error parsing house keeping CPUs\n");
+				exit(EXIT_FAILURE);
+			}
+			break;
 		case 'i':
 			params->stop_us = get_llong_from_str(optarg);
 			break;
@@ -598,6 +612,15 @@ timerlat_top_apply_config(struct osnoise_tool *top, struct timerlat_top_params *
 		}
 	}
 
+	if (params->hk_cpus) {
+		retval = sched_setaffinity(getpid(), sizeof(params->hk_cpu_set),
+					   &params->hk_cpu_set);
+		if (retval == -1) {
+			err_msg("Failed to set rtla to the house keeping CPUs\n");
+			goto out_err;
+		}
+	}
+
 	return 0;
 
 out_err: