Re: [kvm-devel] QEMU PIC indirection patch for in-kernel APIC work

Avi Kivity
2007-04-10T12:17:45Z

Evgeniy Polyakov wrote:
>> This is what Xen does. It is actually less performant than copying, IIRC.
>>
>> The problem with flipping pages around is that physical addresses are
>> cached both in the kvm mmu and in the on-chip tlbs, necessitating
>> expensive page table walks and tlb invalidation IPIs.
>>
>
> Hmm, I'm not familiar with Xen driver, but similar technique was used
> with zero-copy network sniffer some time ago, substituting userspace
> pages with pages containing skb data was about 25-50% faster than
> copying 1500 bytes in general, and in order of 10 times faster in some
> cases.
>
> Check a link please in case we are talking about different ideas:
> http://marc.info/?l=linux-netdev&m=112262743505711&w=2
>
>

I don't really understand what you're testing there. in particular, how
can the copying time change so dramatically depending on whether you've
just rebooted or not?

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