Hi,
is it just me imagining things, or is the RHEL5 HZ value going to be a
regression for userspace; the current rhel5 kernel behavior is that if
userspace asks for a 1ms delay, it gets like a 7ms delay. In RHEL4, the
max delay was 2ms...
An example program to test this is shown below:
#include <stdio.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/time.h>
unsigned long do_time(unsigned long usecs)
{
struct timeval after, before;
int secs, usec;
gettimeofday(&before, NULL);
usleep(usecs);
gettimeofday(&after, NULL);
secs = after.tv_sec - before.tv_sec;
usec = after.tv_usec - before.tv_usec;
return secs * 1000000 + usec;
}
int main(int argc, char **argv)
{
unsigned long delays = 0;
int i;
/* take the average over 100 measurements */
for (i = 0; i < 100; i++)
delays += do_time(1000);
delays = delays / 100;
/* we asked for a 1.000 msec delay, if this takes more than 2.5 msec
that's
an unacceptable quality of service for telco */
if (delays > 2500) {
printf("Unacceptable long delay; asked for 1000 usec, got %i
usec \n", delays);
exit(EXIT_FAILURE);
}
delays = 0;
for (i = 0; i < 100; i++)
delays += do_time(2000);
delays = delays / 100;
printf("%li -> %li \n", 2000, delays);
/* we asked for a 2.000 msec delay, if this takes more than 3.5 msec
that's
an unacceptable quality of service for telco */
if (delays > 3500) {
printf("Unacceptable long delay; asked for 2000 usec, got %i
usec \n", delays);
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
--
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via
http://www.linuxfirmwarekit.org
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