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

On Tue, Apr 10, 2007 at 02:21:24PM +0300, Avi Kivity (avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org) wrote:

quoted

You want to implement zero-copy network device between host and guest, if
I understood this thread correctly?
So, for sending part, device allocates pages from receiver's memory (or
from shared memory), receiver gets an 'interrupt' and got pages from own
memory, which are attached to new skb and transferred up to the network
stack.
It can be extended to use shared ring of pages.
 

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

-- 
	Evgeniy Polyakov

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Evgeniy Polyakov wrote:

quoted

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