On Mon, 2011-06-27 at 15:54 -0700, David Miller wrote: > From: Shirley Ma <mashirle@xxxxxxxxxx> > Date: Mon, 27 Jun 2011 08:45:10 -0700 > > > To support skb zero-copy, a pointer is needed to add to skb share > info. > > Do you agree with this approach? If not, do you have any other > > suggestions? > > I really can't form an opinion unless I am shown the complete > implementation, what this give us in return, what the impact is, etc. zero-copy skb buffers can save significant CPUs. Right now, I only implements macvtap/vhost zero-copy between KVM guest and host. The performance is as follow: Single TCP_STREAM 120 secs test results 2.6.39-rc3 over ixgbe 10Gb NIC results: Message BW(Gb/s)qemu-kvm (NumCPU)vhost-net(NumCPU) PerfTop irq/s 4K 7408.57 92.1% 22.6% 1229 4K(Orig)4913.17 118.1% 84.1% 2086 8K 9129.90 89.3% 23.3% 1141 8K(Orig)7094.55 115.9% 84.7% 2157 16K 9178.81 89.1% 23.3% 1139 16K(Orig)8927.1 118.7% 83.4% 2262 64K 9171.43 88.4% 24.9% 1253 64K(Orig)9085.85 115.9% 82.4% 2229 You can see the overall CPU saved 50% w/i zero-copy. The impact is every skb allocation consumed one more pointer in skb share info, and a pointer check in skb release when last reference is gone. For skb clone, skb expand private head and skb copy, it still keeps copy the buffers to kernel, so we can avoid user application, like tcpdump to hold the user-space buffers too long. Thanks Shirley -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
