I noticed that gettimeofday in RHEL4.6 guests is taking much longer than
with RHEL3.8 guests. I wrote a simple program (see below) to call
gettimeofday in a loop 1,000,000 times and then used time to measure how
long it took.
For the RHEL3.8 guest:
time -p ./timeofday_bench
real 0.99
user 0.12
sys 0.24
For the RHEL4.6 guest with the default clock source (pmtmr):
time -p ./timeofday_bench
real 15.65
user 0.18
sys 15.46
and RHEL4.6 guest with PIT as the clock source (clock=pit kernel parameter):
time -p ./timeofday_bench
real 13.67
user 0.21
sys 13.45
So, basically gettimeofday() takes about 50 times as long on a RHEL4 guest.
Host is a DL380G5, 2 dual-core Xeon 5140 processors, 4 GB of RAM. It's
running kvm.git tree as of 11/18/08 with kvm-75 userspace. Guest in both
RHEL3 and RHEL4 cases has 4 vcpus, 3.5GB of RAM.
david
----------
timeofday_bench.c:
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
int rc = 0, n;
struct timeval tv;
int iter = 1000000; /* number of times to call gettimeofday */
if (argc > 1)
iter = atoi(argv[1]);
if (iter == 0) {
fprintf(stderr, "invalid number of iterations\n");
return 1;
}
printf("starting.... ");
for (n = 0; n < iter; ++n) {
if (gettimeofday(&tv, NULL) != 0) {
fprintf(stderr, "\ngettimeofday failed\n");
rc = 1;
break;
}
}
if (!rc)
printf("done\n");
return rc;
}
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