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 usage
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:
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.
It has integrated V5 review comments from MST and
Michał Mirosław <[email protected]>
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 remove
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 of
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 userspace
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
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.
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(-)
On Sat, May 28, 2011 at 12:14:37PM -0700, Shirley Ma wrote:
> 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 usage
> 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:
>
> 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.
>
> It has integrated V5 review comments from MST and
> Michał Mirosław <[email protected]>
> 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 remove
> 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 of
> 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?
Yes, we do. IMHO the right approach is to wait
for DMAs to be done - just use a sleep/wake up construct,
not a timed sleep.
> 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 userspace
> 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
> 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.
>
> 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(-)
>
>
> --
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