From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shirley Ma Subject: [PATCH V7 0/4 net-next] macvtap/vhost TX zero-copy support Date: Sat, 28 May 2011 12:14:37 -0700 Message-ID: <1306610077.5180.78.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: David Miller , mst@redhat.com, Eric Dumazet , Avi Kivity , Arnd Bergmann Return-path: Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 about 50% CPU usag= e for single stream test on the host, while 4K message size BW has increased about 50%). 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:=20 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 outstandin= g 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. It has integrated V5 review comments from MST and=20 Micha=C5=82 Miros=C5=82aw 1. Prevent userspace apps from holding skb userspace buffers by copying userspace buffers to kernel in skb_clone, skb_copy, pskb_copy, pskb_expand_head. 2. It is also used HIGHDMA, SG feature bits to enable ZEROCOPY to remov= e the dependency of a new feature bit, we can add it later when new feature bit is available. It has integrated V6 review comments from Eric Dumazet. 1. Moving ubuf_info object from skb to caller, just use one pointer in skb_share_info to point ubuf_info object. 2. Change the zero-copy size from 256 bytes to PAGE_SIZE (4K) because o= f the small message size performance issue. 3. During vhost shutting down, release outstanding userspace buffers w/= o waiting for lower device DMAs done if any. Do we really care about the possible wrong data being sent on the wire during shutting down? This patchset includes: 1/4: Add a new sock zero-copy flag, SOCK_ZEROCOPY; 2/4: 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; Or whenever skb_clone, skb_copy= , pskb_copy, pskb_expand_head get call from tcpdump, filtering, these userspace buffers will be copied into kernel ... we don't want userspac= e apps to hold userspace buffers too long. 3/4: 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. 4/4: Add macvtap zero-copy in lower device when sending packet is greater than PAGE_SIZE. The patchset is built against linux-2.6.39. It has passed netperf/netserver multiple streams stress test, tcpdump suspended test, dynamically SG change test. 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 =20 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 =46or 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. drivers/net/macvtap.c | 131 ++++++++++++++++++++++++++++++++++++++++++++---- drivers/vhost/net.c | 45 ++++++++++++++++- drivers/vhost/vhost.c | 51 +++++++++++++++++++ drivers/vhost/vhost.h | 15 ++++++ include/linux/skbuff.h | 25 +++++++++ include/net/sock.h | 1 + net/core/skbuff.c | 83 ++++++++++++++++++++++++++++++- 7 files changed, 338 insertions(+), 13 deletions(-)