Re: [Question]About KVM network zero-copy feature!

On Fri, 10 Aug 2012 11:34:32 +0800
"Peter Huang(Peng)" [off-list ref] wrote:

quoted

I searched from git-log, and found that until now we have vhost TX zero-copy experiment feature, how
about RX zero-copy?

On 08/11/2012 04:55 PM, Stephen Hemminger wrote:

There is no guarantee that packet will ever be read by receiver. This means zero-copy could
create memory back pressure stalls.

It would be handy if this could be an optional feature, perhaps not 
enabled by default due to the problem with stalls you mentioned. I would 
love to see RX zero-copy implemented natively in KVM, as it might 
alleviate the need for custom solutions like vPF_RING:

http://www.ntop.org/products/pf_ring/vpf_ring/

Every time a packet is copied, especially from kernel space to user 
space, there is an opportunity for it to be dropped on its way to the 
receiving application - which is unacceptable when monitoring high-speed 
networks for security or bandwidth accounting purposes.

I am attempting to find a highly-efficient way to deploy virtualized 
network monitoring sensors (Snort, for example). Ideally I want to 
exploit symmetric hardware-based RSS and SR-IOV functionality for 
load-balancing and packet distribution completely in ASIC. I've found 
other existing work in this area (also using custom drivers) indicating 
significant performance gains in the non-virtualized case:

http://www.ndsl.kaist.edu/~shinae/papers/TR-symRSS.pdf

Is there any interest in exploring native RX zero-copy within the 
mainline KVM networking code?

Thanks,
Robert Vineyard