126 lines
3.7 KiB
C
126 lines
3.7 KiB
C
#include <stdio.h>
|
|
#include <poll.h>
|
|
#include <fcntl.h>
|
|
#include <sys/stat.h>
|
|
#include <stdlib.h>
|
|
#include <unistd.h>
|
|
#include <string.h>
|
|
|
|
#define CPU_TRACKING_WINDOW_SECS 1
|
|
#define IO_TRACKING_WINDOW_SECS 1
|
|
#define CPU_TRIGGER_THRESHOLD_MS 100
|
|
#define IO_TRIGGER_THRESHOLD_MS 100
|
|
#define CPU_PRESSURE_FILE "/proc/pressure/cpu"
|
|
#define IO_PRESSURE_FILE "/proc/pressure/io"
|
|
#define FD_CPU_IDX 0
|
|
#define FD_IO_IDX 1
|
|
|
|
struct pollfd fds[2];
|
|
|
|
/*
|
|
One function that prints the system call and the error details
|
|
and then exits with error code 1. Non-zero meaning things didn't go well.
|
|
*/
|
|
void fatal_error(const char *syscall)
|
|
{
|
|
perror(syscall);
|
|
exit(1);
|
|
}
|
|
|
|
/*
|
|
* PSI allows programs to wait for events related to pressure stalls
|
|
* via poll() so that they can avoid continuously polling files in the
|
|
* /proc/pressure directory.
|
|
*
|
|
* We setup to be notified via poll for two types of PSI events, one
|
|
* for CPU and the other for I/O.
|
|
*
|
|
* */
|
|
|
|
void setup_polling() {
|
|
/* Let's first setup our CPU PSI trigger */
|
|
fds[FD_CPU_IDX].fd = open(CPU_PRESSURE_FILE, O_RDWR | O_NONBLOCK);
|
|
if (fds[FD_CPU_IDX].fd < 0)
|
|
fatal_error("open(): " CPU_PRESSURE_FILE);
|
|
|
|
/* Next, our I/O PSI trigger */
|
|
fds[FD_IO_IDX].fd = open(IO_PRESSURE_FILE, O_RDWR | O_NONBLOCK);
|
|
if (fds[FD_IO_IDX].fd < 0)
|
|
fatal_error("open(): " IO_PRESSURE_FILE);
|
|
|
|
fds[FD_CPU_IDX].events = fds[FD_IO_IDX].events = POLLPRI;
|
|
|
|
char trigger[128];
|
|
snprintf(trigger, 128, "some %d %d", CPU_TRIGGER_THRESHOLD_MS * 1000, CPU_TRACKING_WINDOW_SECS * 1000000);
|
|
printf("Trigger: %s\n", trigger);
|
|
if (write(fds[FD_CPU_IDX].fd, trigger, strlen(trigger) + 1) < 0)
|
|
fatal_error("write(): " CPU_PRESSURE_FILE);
|
|
snprintf(trigger, 128, "some %d %d", IO_TRIGGER_THRESHOLD_MS * 1000, IO_TRACKING_WINDOW_SECS * 1000000);
|
|
printf("Trigger: %s\n", trigger);
|
|
if (write(fds[FD_IO_IDX].fd, trigger, strlen(trigger) + 1) < 0)
|
|
fatal_error("write(): " IO_PRESSURE_FILE);
|
|
}
|
|
|
|
|
|
/*
|
|
* This is the main function where we wait for notifications from
|
|
* PSI. We increment 2 separate variables that track CPU and I/O
|
|
* notification counts separately and print them.
|
|
* */
|
|
|
|
void wait_for_notification() {
|
|
int cpu_event_counter = 1;
|
|
int io_event_counter = 1;
|
|
|
|
while (1) {
|
|
int n = poll(fds, 2, -1);
|
|
if (n < 0) {
|
|
fatal_error("poll()");
|
|
}
|
|
|
|
for (int i = 0; i < 2; i++) {
|
|
|
|
/* If the fd of the current iteration does not have any
|
|
* events, move on to the next fd.
|
|
* */
|
|
if (fds[i].revents == 0)
|
|
continue;
|
|
|
|
if (fds[i].revents & POLLERR) {
|
|
fprintf(stderr, "Error: poll() event source is gone.\n");
|
|
exit(1);
|
|
}
|
|
if (fds[i].revents & POLLPRI) {
|
|
if (i == FD_CPU_IDX)
|
|
printf("CPU PSI event %d triggered.\n", cpu_event_counter++);
|
|
else
|
|
printf("I/O PSI event %d triggered.\n", io_event_counter++);
|
|
} else {
|
|
fprintf(stderr, "Unrecognized event: 0x%x.\n", fds[i].revents);
|
|
exit(1);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* We check for tell-tale signs of the running kernel supporting PSI.
|
|
* Else, we print a friendly message and exit.
|
|
* */
|
|
|
|
void check_basics() {
|
|
struct stat st;
|
|
int sret = stat(CPU_PRESSURE_FILE, &st);
|
|
if (sret == -1) {
|
|
fprintf(stderr, "Error! Your kernel does not expose pressure stall information.\n");
|
|
fprintf(stderr, "You may want to check if you have Linux Kernel v5.2+ with PSI enabled.\n");
|
|
exit(1);
|
|
}
|
|
}
|
|
|
|
int main() {
|
|
check_basics();
|
|
setup_polling();
|
|
wait_for_notification();
|
|
return 0;
|
|
} |