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

Avi Kivity
2008-04-16T08:46:41Z

David S. Ahern wrote:
> I have been looking at RHEL3 based guests lately, and to say the least the
> performance is horrible. Rather than write a long tome on what I've done and
> observed, I'd like to find out if anyone has some insights or known problem
> areas running 2.4 guests. The short of it is that % system time spikes from time
> to time (e.g., on exec of a new process such as running /bin/true).
>
> I do not see the problem running RHEL3 on ESX, and an equivalent VM running
> RHEL4 runs fine. That suggests that the 2.4 kernel is doing something in a way
> that is not handled efficiently by kvm.
>
> Can someone shed some light on it?
>

It's not something that I test regularly. If you're running a 32-bit
kernel, I'd suspect kmap(), or perhaps false positives from the fork
detector.

kvmtrace will probably give enough info to tell exactly what's going on;
'kvmstat -1' while the badness is happening may also help.

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