[yocto] Yocto Realtime tests on beaglebone black
Stephen Flowers
sflowers1 at gmail.com
Tue Feb 10 06:39:44 PST 2015
Thanks for your input. Here are results of 1000 samples over a 10
second period:
Interrupt response (microseconds)
standard: min: 81, max:118, average: 84
rt: min: 224, max: 289, average: 231
Will share the .config later once I get on that machine.
Steve
On 10/02/2015 14:16, Bruce Ashfield wrote:
> On 15-02-10 08:06 AM, Stephen Flowers wrote:
>> Hi All,
>>
>> I have built the realtime kernel using Yocto and deployed on the
>> beaglebone black (specifically core-image-rt-sdk). I have written a
>> program to test the timer latency and interrupt latency of userspace
>> applications. For this I'm using a simple timerfd to generate a
>> periodic 10ms gpio toggle which itself acts as a gpio interrupt on
>> another gpio pin.
>> I find the latency is much worse on the preempt_rt kernel than the
>> standard one. RT kernel gives around 220us average with the standard
>> kernel about 80us. Testing with Xenomai gives about 60us. The response
>> times are measured with an external logic analyser, and taken with no
>> other load on the system. Kernel version is 3.14.
>>
>> The difference between standard and RT kernel configs:
>> Preemption model: desktop vs. realtime kernel
>> Timer: 100Hz vs 1000Hz
>> High resolution timers disabled
>
> Can you share the full .config for both configurations ? That should
> shed a bit more light on what might be misconfigured.
>
> I haven't run tests on the beaglebone black myself, but on similar
> ARM boards, performance has been as expected.
>
> You are talking about average latency above, what about the max
> latency ? We expect that the preempt-rt kernel will have a higher
> minimum, and often average latency .. but will be significantly
> better in maximum latency.
>
> It would also be useful to grab cyclictest results for the standard
> and preempt-rt kernel as a baseline performance measure.
>
> Bruce
>
>>
>> I'm having a hard time figuring out why the RT kernel gives worse
>> latency. Anyone have any insight into this?
>> Included the source code below.
>>
>> Thanks & Regards,
>> Steve
>>
>> #include<sys/time.h>
>> #include<time.h>
>> #include<sys/types.h>
>> #include <signal.h>
>> #include <stdlib.h>
>> #include <stdio.h>
>> #include <sched.h>
>> #include <sys/mman.h>
>> #include "poll.h"
>> #include "fcntl.h"
>> #include "string.h"
>> #include "errno.h"
>> #include <sys/timerfd.h>
>>
>> #define TIMER_OUT_PATH "/sys/class/gpio/gpio47"
>> #define LED_OUT_PATH "/sys/class/gpio/gpio26"
>> #define IRQ_IN_PATH "/sys/class/gpio/gpio46"
>>
>> static int timer_toggle = 0;
>> static int output_toggle = 0;
>>
>> void stack_prefault(void)
>> {
>> unsigned char dummy[8192];
>> memset(dummy, 0, 8192);
>> }
>>
>>
>> int main(int argc, char* argv[])
>> {
>> struct itimerspec itv;
>> unsigned long long timer_increment = 0;
>>
>> clock_t prevClock;
>> int sigCnt = 0;
>> struct sigaction sa;
>> struct sched_param sp;
>>
>> struct pollfd fdset[2];
>> int fd_in;
>> int action;
>> int fd_led;
>> int fd_timer_out;
>> int fd_timer_in;
>>
>> char buf[2];
>> int len;
>>
>> // setup gpio
>> if(system("echo 46 > /sys/class/gpio/export") == -1)
>> perror("unable to export gpio 46");
>>
>> if(system("echo 47 > /sys/class/gpio/export") == -1)
>> perror("unable to export gpio 47");
>>
>> if(system("echo 26 > /sys/class/gpio/export") == -1)
>> perror("unable to export gpio 26");
>>
>> // timer out
>> if(system("echo out > /sys/class/gpio/gpio47/direction") == -1)
>> perror("unable to set 47 to output");
>>
>> // led out
>> if(system("echo out > /sys/class/gpio/gpio26/direction") == -1)
>> perror("unable to set 26 to output");
>>
>> // irq in
>> if(system("echo in > /sys/class/gpio/gpio46/direction") == -1)
>> perror("unable to set 46 to input");
>>
>> if(system("echo both > /sys/class/gpio/gpio46/edge") == -1)
>> perror("unable to set 46 edge");
>>
>> // set scheduling parameters
>> sp.sched_priority = sched_get_priority_max(SCHED_FIFO);
>> if(sched_setscheduler(0, SCHED_FIFO, &sp) == -1)
>> {
>> perror("setscheduler");
>> exit(-1);
>> }
>>
>> // lock memory
>> if(mlockall(MCL_CURRENT|MCL_FUTURE) == -1)
>> perror("mlockall");
>>
>> stack_prefault();
>>
>> // Set up timer
>> fd_timer_in = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK);
>> printf("fd_timer:%d\n",fd_timer_in);
>>
>> if(fd_timer_in < 0)
>> {
>> perror("timerfd_create()");
>> }
>>
>> itv.it_value.tv_sec = 0;
>> itv.it_value.tv_nsec = 10000000;
>> itv.it_interval.tv_sec = 0;
>> itv.it_interval.tv_nsec = 10000000;
>> if(-1 == timerfd_settime(fd_timer_in, 0, &itv, NULL))
>> {
>> perror("settime()");
>> }
>>
>> // setup file descriptor for poll()
>> fd_in = open(IRQ_IN_PATH "/value", O_RDONLY | O_NONBLOCK);
>> printf("fd irq input:%d\n",fd_in);
>>
>> if(fd_in < 0)
>> {
>> perror("file open problem");
>> exit(0);
>> }
>>
>> while(1)
>> {
>> memset((void*)fdset, 0, sizeof(fdset));
>> fdset[0].fd = fd_in;
>> fdset[0].events = POLLPRI | POLLERR;
>> fdset[0].revents = 0;
>>
>> fdset[1].fd = fd_timer_in;
>> fdset[1].events = POLLIN | POLLERR;
>> fdset[1].revents = 0;
>> action = poll(fdset, 2, -1);
>>
>> if(action < 0)
>> {
>> if(errno == EINTR)
>> {
>> // when signal interrupts poll, we poll again
>> continue;
>> }
>> else
>> {
>> perror("poll failed");
>> exit(0);
>> }
>> }
>>
>> if(fdset[1].revents & POLLIN)
>> {
>> //len = read(fdset[1].fd, 0, SEEK_SET);
>> len = read(fdset[1].fd, &timer_increment,
>> sizeof(timer_increment));
>>
>> fd_timer_out = open( TIMER_OUT_PATH "/value", O_WRONLY);
>>
>> if(timer_toggle ^= 1)
>> {
>> write(fd_timer_out, "1", 2);
>> }
>> else
>> {
>> write(fd_timer_out, "0", 2);
>> }
>>
>> close(fd_timer_out);
>> }
>>
>> if(fdset[0].revents & POLLPRI)
>> {
>> lseek(fdset[0].fd, 0, SEEK_SET); // read from start
>> of file
>> len = read(fdset[0].fd, buf, sizeof(buf));
>>
>> fd_led = open( LED_OUT_PATH "/value", O_WRONLY |
>> O_NONBLOCK);
>>
>> if(buf[0] == '1')
>> {
>> write(fd_led, "1", 2);
>> }
>> else
>> {
>> write(fd_led, "0", 2);
>> }
>>
>> close(fd_led);
>> }
>> }
>>
>> close(fd_in);
>> close(fd_timer_in);
>> close(fd_led);
>> printf("finished\n");
>> return 0;
>> }
>>
>>
>>
>>
>>
>
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