On 06/25/2009 04:25 PM, Eran Rom wrote:
Hi All,
Am a newbie (to kvm, linux kernel, git, etc.) so apologize in advance for
missing/inaccurate info.
I am experiencing inconsistent behavior of guest gettimeofday, described below.
I have seen prior reference to the problem, however, it was not clear whether
the issue was solved or not and where.
Below is a description of my setup and the behavior I see.
Another question is whether oprofile with timer mode would suffer from the same
problem?
Otherwise I saw that kvm-85 has "generic performance counter msr handling", does
this mean that oprofile can be executed without the timer mode?
Thanks very much,
Eran
Setup:
Guest 32 bit ubuntu with 2.6.27 kernel
Host 64 bit Suse 10.2 with 2.6.27 kernel
1 quadcore Intel Xeon CPU
I am not sure about the kvm userspace code version.
Used git to create a repository, and then did
git checkout kvm-updates-2.6.27 (is that fixed in time?)
Behavior:
Running a code doing:
t1 = gettimeofday
t2 = gettimeofday
while t2-t1< 5 minutes {
sleep(1)
t2 = gettimeofday
}
Ran it 10 times, each time in a 'newly launched' VM, halting it after the test.
8 out of 10 times the wall clock showed 5 minutes
1 time 4 minutes and 40 seconds
1 time 0 seconds
I'm not sure what's your 'wall clock' value, there is not printf in your
script.
Nevertheless, the tsc clock is not reliable, the host can scale it, or
go into
deep sleep state.
So either use newer kernel with kvmclock (pv) or change the clock source
into rtc/pit
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
