Re: QEMU PIC indirection patch for in-kernel APIC work

Avi Kivity
2007-04-04T16:58:34Z

Nakajima, Jun wrote:
> I compared the performance on Xen and KVM for kernel build using the
> same guest image. Looks like KVM was (kvm-17) three times slower as far
> as we tested, and that high load of qemu was one of the symptoms. We are
> looking at the shadow code, but the load of qemu looks very high. I
> remember we had similar problems in Xen before, but those were fixed.
> Someone should take a look at the qemu side.
>

I'd expect the following issues to dominate:

- the shadow cache is quite small at 256 pages. Increasing it may
increase performance.

- we haven't yet taught the scheduler that migrating vcpus is expensive
due to the IPI needed to fetch the vmcs. Maybe running with 'taskset 1'
would help

- shadow eviction policy is FIFO, not LRU, which probably causes many
page faults.

Running kvm_stat can help show what's going on.

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