This patchset add supports for TX zero-copy between guest and host kernel through vhost. It significantly reduces CPU utilization on the local host on which the guest is located (It reduced 30-50% CPU usage for vhost thread for single stream test). The patchset is based on previous submission and comments from the community regarding when/how to handle guest kernel buffers to be released. This is the simplest approach I can think of after comparing with several other solutions. This patchset has integrated V3 review comments from community: 1. Add more comments on how to use device ZEROCOPY flag; 2. Change device ZEROCOPY to available bit 31 3. Fix skb header linear allocation when virtio_net GSO is not enabled It has integrated V4 review comments from MST and Sridhar: 1. In vhost, using socket poll wake up for outstanding DMAs 2. Add detailed comments for vhost_zerocopy_signal_used call 3. Add sleep in vhost shutting down instead of busy-wait for outstanding DMAs. 4. Copy small packets, don't do zero-copy callback in mavtap, mark it's DMA done in vhost 5. change zerocopy to bool in macvtap. One comment doesn't address: Should we count the whole page in sk_wmem_alloc for zerocopy buffer? If so, sock_wfree needs to change too. This patchset includes: 1/6: Add a new sock zero-copy flag, SOCK_ZEROCOPY; 2/6: Add a new device flag, NETIF_F_ZEROCOPY for lower level device support zero-copy; 3/6: Add a new struct skb_ubuf_info in skb_share_info for userspace buffers release callback when lower device DMA has done for that skb, which is the last reference count gone; 4/6: Add vhost zero-copy callback in vhost when skb last refcnt is gone; add vhost_zerocopy_signal_used to notify guest to release TX skb buffers. 5/6: Add macvtap zero-copy in lower device when sending packet is greater than 256 bytes to make sure there is enough room for expanding skb head. 6/6: example: enable Intel 10Gb NIC zero-copy feature flag The patchset is built against most recent net-next linux 2.6.39-rc7. It has passed netperf/netserver multiple streams stress test. Single TCP_STREAM 120 secs test results 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 For message size less or equal than 2K, there is a known KVM guest TX overrun issue. With this zero-copy patch, the issue becomes more severe, guest io_exits has tripled than before, so the performance is not good. Once the TX overrun problem has been addressed, I will retest the small message size performance. -- 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
