Shu Zhong Hua
Reputation: 9
Linux posix timer cause high total CPU load
I wrote a simple Linux program (timertest) with 500us POSIX timer and running it in Dual-core ARM Cortex-A9 processor. The process timertest takes about 25% CPU load, that's ok. But sometimes the total CPU load is very high (100%). If I kill timertest process, the total CPU load decreased to 1%. I expect the total CPU load is same as timertest process because there is no other high load process running?
I tried with different Linux timer (e.g., setitimer) and top command (e.g., htop, procps-ng top). But it's same result.
- Total CPU load is 100% /
timertestis 25% (htop)
$ timertest
Busy time: 92 us
posix_timer: 0
posix_timer: 1
...
$ htop
0[####****************************100.0%] Tasks: 13, 0 thr, 45 kthr; 1 running
1[# 0.7%] Load average: 0.76 0.25 0.09
Mem[|#*@ 15.3M/1003M] Uptime: 00:02:16
Swp[ 0K/0K]
PID USER PRI NI VIRT RES SHR S CPU%-MEM% TIME+ Command
229 root 20 0 3480 2356 2220 R 25.8 0.2 0:19.73 timertest
231 root 20 0 3216 2428 1828 R 0.7 0.2 0:00.26 htop
1 root 20 0 1580 1172 1088 S 0.0 0.1 0:01.68 init [5]
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp
4 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_par_gp
5 root 20 0 0 0 0 I 0.0 0.0 0:00.00 kworker/0:0-rcu_gp
6 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/0:0H-events_highpr
7 root 20 0 0 0 0 I 0.0 0.0 0:00.00 kworker/u4:0-events_unboun
8 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 mm_percpu_wq
9 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_tasks_rude_
10 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
11 root 20 0 0 0 0 I 0.0 0.0 0:00.01 rcu_sched
12 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
13 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/0
14 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/1
15 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/1
16 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/1
17 root 20 0 0 0 0 I 0.0 0.0 0:00.00 kworker/1:0-events
18 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/1:0H-events_highpr
19 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kdevtmpfs
20 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 netns
21 root 20 0 0 0 0 I 0.0 0.0 0:00.00 kworker/0:1-events_long
22 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khungtaskd
23 root 20 0 0 0 0 S 0.0 0.0 0:00.00 oom_reaper
24 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 writeback
25 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kcompactd0
26 root 20 0 0 0 0 I 0.0 0.0 0:00.05 kworker/u4:1-events_unboun
31 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kblockd
32 root -51 0 0 0 0 S 0.0 0.0 0:00.00 watchdogd
33 root 20 0 0 0 0 I 0.0 0.0 0:00.03 kworker/1:1-mm_percpu_wq
34 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rpciod
35 root 0 -20 0 0 0 I 0.0 0.0 0:00.05 kworker/0:1H-kblockd
36 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/u5:0
37 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 xprtiod
38 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kswapd0
39 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 nfsiod
40 root 20 0 0 0 0 I 0.0 0.0 0:00.04 kworker/0:2-mm_percpu_wq
41 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 stmmac_wq
43 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 ipv6_addrconf
44 root 0 -20 0 0 0 I 0.0 0.0 0:00.03 kworker/1:1H-kblockd
45 root 20 0 0 0 0 I 0.0 0.0 0:00.00 kworker/0:3-events
46 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 mmc_complete
47 root 20 0 0 0 0 S 0.0 0.0 0:00.00 jbd2/mmcblk0p2-
48 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 ext4-rsv-conver
51 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/1:2H
78 root 20 0 2744 1464 1116 S 0.0 0.1 0:00.11 /sbin/udevd -d
95 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kworker/0:2H-mmc_complete
96 root 20 0 0 0 0 I 0.0 0.0 0:00.00 kworker/u4:2-events_unboun
194 root 20 0 2156 1168 1072 S 0.0 0.1 0:03.01 /usr/sbin/dropbear -r /etc
202 root 20 0 2344 1492 1408 S 0.0 0.1 0:00.01 /sbin/syslogd -n -O /var/l
205 root 20 0 2344 1512 1408 S 0.0 0.1 0:00.01 /sbin/klogd -n
209 root 20 0 2100 1180 1084 S 0.0 0.1 0:00.00 /usr/sbin/vsftpd
214 root 20 0 2344 1496 1408 S 0.0 0.1 0:00.00 /bin/sh /bin/start_getty 1
215 root 20 0 2344 1432 1344 S 0.0 0.1 0:00.00 /sbin/getty 38400 tty1
217 root 20 0 2432 1684 1556 S 0.0 0.2 0:00.02 -sh
221 root 20 0 2244 1592 1420 S 0.0 0.2 0:00.25 /usr/sbin/dropbear -r /etc
222 root 20 0 2432 1680 1556 S 0.0 0.2 0:00.01 -sh
- C++ test code (`timertest.cpp`)
#include <csignal>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
namespace {
void busyCpu()
{
volatile long long i;
for (i = 0; i < 9000; ++i)
{
// Loop 9000: 93 us / CPU 23 % (Linux arrow-sockit 5.10.100-altera)
}
}
void posixTimerSignal(int sig, siginfo_t *si, void *pri)
{
static int i = 0;
static int count = 0;
busyCpu();
if (i++ == 2000)
{
::printf("posix_timer: %d\n", count++);
i = 0;
}
}
void posixTimerTest()
{
timer_t timer = {0};
struct sigevent sev = {0};
struct sigaction sa = {0};
const struct timespec timeVal = {
.tv_sec = 0,
.tv_nsec = 500 * 1000 // 500 us
};
const struct itimerspec its =
{
.it_interval = timeVal,
.it_value = timeVal
};
sev.sigev_notify = SIGEV_SIGNAL;
sev.sigev_signo = SIGRTMIN;
sev.sigev_value.sival_ptr = &timer;
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = posixTimerSignal;
if(::sigemptyset(&sa.sa_mask) == -1)
{
::perror("sigemptyset error");
}
if(::sigaction(SIGRTMIN, &sa, nullptr) == -1)
{
::perror("sigaciton error");
}
if(::timer_create(CLOCK_REALTIME, &sev, &timer) != 0)
{
::perror("timer_create error");
}
if(::timer_settime(timer, 0, &its, nullptr) != 0)
{
::perror("timer_settime error");
}
while (true)
{
::pause();
}
}
}
int main(int argc, char* argv[])
{
::printf("Timer test cpp program started\n");
posixTimerTest();
return 0;
}
- Linux version:
$ uname -a
Linux arrow-sockit 5.10.100-altera #1 SMP Tue Jun 14 16:39:33 UTC 2022 armv7l GNU/Linux
- CPU info
$ cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 0 (v7l)
BogoMIPS : 200.00
Features : half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpd32
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x3
CPU part : 0xc09
CPU revision : 0
processor : 1
model name : ARMv7 Processor rev 0 (v7l)
BogoMIPS : 200.00
Features : half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpd32
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x3
CPU part : 0xc09
CPU revision : 0
Hardware : Altera SOCFPGA
Revision : 0000
Serial : 0000000000000000
Update: If I change the timer interval from 500 us to 499 us, the total CPU load is same as process CPU load (24%).
0[* 0.7%] Tasks: 13, 0 thr, 41 kthr; 1 running
1[#######** 23.8%] Load average: 0.01 0.01 0.00
Mem[|#*@ 15.2M/1003M] Uptime: 12:03:14
Swp[ 0K/0K]
PID USER PRI NI VIRT RES SHR S CPU%-MEM% TIME+ Command
437 root 20 0 3480 2356 2220 R 24.5 0.2 0:01.58 ./timertest -p -
355 root 20 0 3088 2312 1828 R 0.7 0.2 0:31.52 htop
1 root 20 0 1580 1172 1088 S 0.0 0.1 0:02.24 init [5]
2 root 20 0 0 0 0 S 0.0 0.0 0:00.01 kthreadd
3 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_gp
4 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rcu_par_gp
8 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 mm_percpu_wq
9 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_tasks_rude_
10 root 20 0 0 0 0 S 0.0 0.0 0:00.12 ksoftirqd/0
11 root 20 0 0 0 0 I 0.0 0.0 0:00.88 rcu_sched
12 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
13 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/0
14 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cpuhp/1
15 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/1
16 root 20 0 0 0 0 S 0.0 0.0 0:00.24 ksoftirqd/1
19 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kdevtmpfs
20 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 netns
22 root 20 0 0 0 0 S 0.0 0.0 0:00.01 khungtaskd
23 root 20 0 0 0 0 S 0.0 0.0 0:00.00 oom_reaper
24 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 writeback
25 root 20 0 0 0 0 S 0.0 0.0 0:01.16 kcompactd0
31 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 kblockd
32 root -51 0 0 0 0 S 0.0 0.0 0:00.11 watchdogd
34 root 0 -20 0 0 0 I 0.0 0.0 0:00.00 rpciod
Upvotes: 0
Views: 83
Answers (0)
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