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Message-ID: <1305573868.3456.18.camel@localhost.localdomain>
Date: Mon, 16 May 2011 12:24:28 -0700
From: Shirley Ma <mashirle@...ibm.com>
To: David Miller <davem@...emloft.net>, mst@...hat.com,
Eric Dumazet <eric.dumazet@...il.com>,
Avi Kivity <avi@...hat.com>, Arnd Bergmann <arnd@...db.de>
Cc: netdev@...r.kernel.org, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH V5 0/6 net-next] macvtap/vhost TX zero-copy support
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.
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