#! /usr/bin/python3
# @lint-avoid-python-3-compatibility-imports
#
# runqlen Summarize scheduler run queue length as a histogram.
# For Linux, uses BCC, eBPF.
#
# This counts the length of the run queue, excluding the currently running
# thread, and shows it as a histogram.
#
# Also answers run queue occupancy.
#
# USAGE: runqlen [-h] [-T] [-Q] [-m] [-D] [interval] [count]
#
# REQUIRES: Linux 4.9+ (BPF_PROG_TYPE_PERF_EVENT support). Under tools/old is
# a version of this tool that may work on Linux 4.6 - 4.8.
#
# Copyright 2016 Netflix, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 12-Dec-2016 Brendan Gregg Created this.
from __future__ import print_function
from bcc import BPF, PerfType, PerfSWConfig, utils
from time import sleep, strftime
from tempfile import NamedTemporaryFile
from os import open, close, dup, unlink, O_WRONLY
import argparse
# arguments
examples = """examples:
./runqlen # summarize run queue length as a histogram
./runqlen 1 10 # print 1 second summaries, 10 times
./runqlen -T 1 # 1s summaries and timestamps
./runqlen -O # report run queue occupancy
./runqlen -C # show each CPU separately
"""
parser = argparse.ArgumentParser(
description="Summarize scheduler run queue length as a histogram",
formatter_class=argparse.RawDescriptionHelpFormatter,
epilog=examples)
parser.add_argument("-T", "--timestamp", action="store_true",
help="include timestamp on output")
parser.add_argument("-O", "--runqocc", action="store_true",
help="report run queue occupancy")
parser.add_argument("-C", "--cpus", action="store_true",
help="print output for each CPU separately")
parser.add_argument("interval", nargs="?", default=99999999,
help="output interval, in seconds")
parser.add_argument("count", nargs="?", default=99999999,
help="number of outputs")
parser.add_argument("--ebpf", action="store_true",
help=argparse.SUPPRESS)
args = parser.parse_args()
countdown = int(args.count)
debug = 0
frequency = 99
# Linux 4.15 introduced a new field runnable_weight
# in linux_src:kernel/sched/sched.h as
# struct cfs_rq {
# struct load_weight load;
# unsigned long runnable_weight;
# unsigned int nr_running, h_nr_running;
# ......
# }
# and this tool requires to access nr_running to get
# runqueue len information.
#
# The commit which introduces cfs_rq->runnable_weight
# field also introduces the field sched_entity->runnable_weight
# where sched_entity is defined in linux_src:include/linux/sched.h.
#
# To cope with pre-4.15 and 4.15/post-4.15 releases,
# we run a simple BPF program to detect whether
# field sched_entity->runnable_weight exists. The existence of
# this field should infer the existence of cfs_rq->runnable_weight.
#
# This will need maintenance as the relationship between these
# two fields may change in the future.
#
def check_runnable_weight_field():
# Define the bpf program for checking purpose
bpf_check_text = """
#include <linux/sched.h>
unsigned long dummy(struct sched_entity *entity)
{
return entity->runnable_weight;
}
"""
# Get a temporary file name
tmp_file = NamedTemporaryFile(delete=False)
tmp_file.close()
# Duplicate and close stderr (fd = 2)
old_stderr = dup(2)
close(2)
# Open a new file, should get fd number 2
# This will avoid printing llvm errors on the screen
fd = open(tmp_file.name, O_WRONLY)
try:
t = BPF(text=bpf_check_text)
success_compile = True
except:
success_compile = False
# Release the fd 2, and next dup should restore old stderr
close(fd)
dup(old_stderr)
close(old_stderr)
# remove the temporary file and return
unlink(tmp_file.name)
return success_compile
# define BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>
#include <linux/sched.h>
// Declare enough of cfs_rq to find nr_running, since we can't #import the
// header. This will need maintenance. It is from kernel/sched/sched.h:
// The runnable_weight field is removed from Linux 5.7.0
struct cfs_rq_partial {
struct load_weight load;
#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 7, 0)
RUNNABLE_WEIGHT_FIELD
#endif
unsigned int nr_running, h_nr_running;
};
typedef struct cpu_key {
int cpu;
unsigned int slot;
} cpu_key_t;
STORAGE
int do_perf_event()
{
unsigned int len = 0;
pid_t pid = 0;
struct task_struct *task = NULL;
struct cfs_rq_partial *my_q = NULL;
// Fetch the run queue length from task->se.cfs_rq->nr_running. This is an
// unstable interface and may need maintenance. Perhaps a future version
// of BPF will support task_rq(p) or something similar as a more reliable
// interface.
task = (struct task_struct *)bpf_get_current_task();
my_q = (struct cfs_rq_partial *)task->se.cfs_rq;
len = my_q->nr_running;
// Calculate run queue length by subtracting the currently running task,
// if present. len 0 == idle, len 1 == one running task.
if (len > 0)
len--;
STORE
return 0;
}
"""
# code substitutions
if args.cpus:
bpf_text = bpf_text.replace('STORAGE',
'BPF_HISTOGRAM(dist, cpu_key_t, MAX_CPUS);')
bpf_text = bpf_text.replace('STORE', 'cpu_key_t key = {.slot = len}; ' +
'key.cpu = bpf_get_smp_processor_id(); ' +
'dist.increment(key);')
else:
bpf_text = bpf_text.replace('STORAGE',
'BPF_HISTOGRAM(dist, unsigned int);')
bpf_text = bpf_text.replace('STORE', 'dist.atomic_increment(len);')
# If target has BTF enabled, use BTF to check runnable_weight field exists in
# cfs_rq first, otherwise fallback to use check_runnable_weight_field().
if BPF.kernel_struct_has_field(b'cfs_rq', b'runnable_weight') == 1 \
or check_runnable_weight_field():
bpf_text = bpf_text.replace('RUNNABLE_WEIGHT_FIELD', 'unsigned long runnable_weight;')
else:
bpf_text = bpf_text.replace('RUNNABLE_WEIGHT_FIELD', '')
if debug or args.ebpf:
print(bpf_text)
if args.ebpf:
exit()
num_cpus = len(utils.get_online_cpus())
# initialize BPF & perf_events
b = BPF(text=bpf_text, cflags=['-DMAX_CPUS=%s' % str(num_cpus)])
b.attach_perf_event(ev_type=PerfType.SOFTWARE,
ev_config=PerfSWConfig.CPU_CLOCK, fn_name="do_perf_event",
sample_period=0, sample_freq=frequency)
print("Sampling run queue length... Hit Ctrl-C to end.")
# output
exiting = 0 if args.interval else 1
dist = b.get_table("dist")
while (1):
try:
sleep(int(args.interval))
except KeyboardInterrupt:
exiting = 1
print()
if args.timestamp:
print("%-8s\n" % strftime("%H:%M:%S"), end="")
if args.runqocc:
if args.cpus:
# run queue occupancy, per-CPU summary
idle = {}
queued = {}
cpumax = 0
for k, v in dist.items():
if k.cpu > cpumax:
cpumax = k.cpu
for c in range(0, cpumax + 1):
idle[c] = 0
queued[c] = 0
for k, v in dist.items():
if k.slot == 0:
idle[k.cpu] += v.value
else:
queued[k.cpu] += v.value
for c in range(0, cpumax + 1):
samples = idle[c] + queued[c]
if samples:
runqocc = float(queued[c]) / samples
else:
runqocc = 0
print("runqocc, CPU %-3d %6.2f%%" % (c, 100 * runqocc))
else:
# run queue occupancy, system-wide summary
idle = 0
queued = 0
for k, v in dist.items():
if k.value == 0:
idle += v.value
else:
queued += v.value
samples = idle + queued
if samples:
runqocc = float(queued) / samples
else:
runqocc = 0
print("runqocc: %0.2f%%" % (100 * runqocc))
else:
# run queue length histograms
dist.print_linear_hist("runqlen", "cpu")
dist.clear()
countdown -= 1
if exiting or countdown == 0:
exit()
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