High scheduler wake up times

From: Shawn Bohrer
Date: Sat Jan 30 2010 - 18:46:55 EST


Currently we have a workload that depends on around 50 processes that
wake up 1000 times a second do a small amount of work and go back to
sleep. This works great on RHEL 5 (2.6.18-164.6.1.el5), but on recent
kernels we are unable to achieve 1000 iterations per second. Using
the simple test application below on RHEL 5 2.6.18-164.6.1.el5 I can run
500 of these processes on and still achieve 999.99 iterations per
second. Running just 10 of these processes on the same machine with produces results like:

Iterations Per Sec: 905.659667
Iterations Per Sec: 805.099068
Iterations Per Sec: 925.195578
Iterations Per Sec: 759.310773
Iterations Per Sec: 702.849261
Iterations Per Sec: 782.157292
Iterations Per Sec: 917.138031
Iterations Per Sec: 834.770391
Iterations Per Sec: 850.543755

I've tried playing with some of the cfs tunables in /proc/sys/kernel/
without success. Are there any suggestions on how to achieve the
results we are looking for using a recent kernel?


#include <sys/epoll.h>
#include <sys/time.h>
#include <stdio.h>
#include <unistd.h>

int main ()
int epfd = epoll_create(1);
int i, j;
struct timeval tv;
unsigned long start, end;
const unsigned int count = 60000;

while (1) {
gettimeofday(&tv, NULL);
start = tv.tv_sec * 1000000 + tv.tv_usec;

for (i = 0; i < count; ++i) {
if (epoll_wait(epfd, 0, 1, 1) == -1)
perror("epoll failed");

for (j = 0; j < 10000; ++j)
/* simulate work */;
gettimeofday(&tv, NULL);
end = tv.tv_sec * 1000000 + tv.tv_usec;

printf("Iterations Per Sec: %f\n", count/((double)(end - start)/1000000));


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