Re: performance with guests running 2.4 kernels (specifically RHEL3)

Avi Kivity
2008-05-13T07:25:38Z

David S. Ahern wrote:
> That does the trick with kscand.
>
>

Not so fast... the patch updates the flood count to 5. Can you check
if a lower value still works? Also, whether updating the flood count to
5 (without the rest of the patch) works?

Unconditionally bumping the flood count to 5 will likely cause a
performance regression on other guests.

While I was able to see excessive flooding, I couldn't reproduce your
kscand problem. Running /bin/true always returned immediately for me.

> Do you have recommendations for clock source settings? For example in my
> test case for this patch the guest gained 73 seconds (ahead of real
> time) after only 3 hours, 5 min of uptime.
>

The kernel is trying to correlate tsc and pit, which isn't going to work.

Try disabling the tsc, set edx.bit4=0 for cpuid.eax=1 in qemu-kvm-x86
.c do_cpuid_ent().

--
error compiling committee.c: too many arguments to function

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