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1#!/usr/bin/env python3
2# SPDX-License-Identifier: GPL-2.0-only
3#
4# Copyright (C) 2024 Red Hat, Inc. Daniel Bristot de Oliveira <[email protected]>
5#
6# This is a sample code about how to use timerlat's timer by any workload
7# so rtla can measure and provide auto-analysis for the overall latency (IOW
8# the response time) for a task.
9#
10# Before running it, you need to dispatch timerlat with -U option in a terminal.
11# Then # run this script pinned to a CPU on another terminal. For example:
12#
13# timerlat_load.py 1 -p 95
14#
15# The "Timerlat IRQ" is the IRQ latency, The thread latency is the latency
16# for the python process to get the CPU. The Ret from user Timer Latency is
17# the overall latency. In other words, it is the response time for that
18# activation.
19#
20# This is just an example, the load is reading 20MB of data from /dev/full
21# It is in python because it is easy to read :-)
22
23import argparse
24import sys
25import os
26
27parser = argparse.ArgumentParser(description='user-space timerlat thread in Python')
28parser.add_argument("cpu", type=int, help='CPU to run timerlat thread')
29parser.add_argument("-p", "--prio", type=int, help='FIFO priority')
30args = parser.parse_args()
31
32try:
33 affinity_mask = {args.cpu}
34 os.sched_setaffinity(0, affinity_mask)
35except Exception as e:
36 print(f"Error setting affinity: {e}")
37 sys.exit(1)
38
39if args.prio:
40 try:
41 param = os.sched_param(args.prio)
42 os.sched_setscheduler(0, os.SCHED_FIFO, param)
43 except Exception as e:
44 print(f"Error setting priority: {e}")
45 sys.exit(1)
46
47try:
48 timerlat_path = f"/sys/kernel/tracing/osnoise/per_cpu/cpu{args.cpu}/timerlat_fd"
49 timerlat_fd = open(timerlat_path, 'r')
50except PermissionError:
51 print("Permission denied. Please check your access rights.")
52 sys.exit(1)
53except OSError:
54 print("Error opening timerlat fd, did you run timerlat -U?")
55 sys.exit(1)
56
57try:
58 data_fd = open("/dev/full", 'r')
59except Exception as e:
60 print(f"Error opening data fd: {e}")
61 sys.exit(1)
62
63while True:
64 try:
65 timerlat_fd.read(1)
66 data_fd.read(20 * 1024 * 1024)
67 except KeyboardInterrupt:
68 print("Leaving")
69 break
70 except IOError as e:
71 print(f"I/O error occurred: {e}")
72 break
73 except Exception as e:
74 print(f"Unexpected error: {e}")
75 break
76
77timerlat_fd.close()
78data_fd.close()