On 1/17/25 14:28, Paolo Abeni wrote:
On 1/17/25 12:16 AM, David Wei wrote:
This patchset adds support for zero copy rx into userspace pages using
io_uring, eliminating a kernel to user copy.
We configure a page pool that a driver uses to fill a hw rx queue to
hand out user pages instead of kernel pages. Any data that ends up
hitting this hw rx queue will thus be dma'd into userspace memory
directly, without needing to be bounced through kernel memory. 'Reading'
data out of a socket instead becomes a _notification_ mechanism, where
the kernel tells userspace where the data is. The overall approach is
similar to the devmem TCP proposal.
This relies on hw header/data split, flow steering and RSS to ensure
packet headers remain in kernel memory and only desired flows hit a hw
rx queue configured for zero copy. Configuring this is outside of the
scope of this patchset.
We share netdev core infra with devmem TCP. The main difference is that
io_uring is used for the uAPI and the lifetime of all objects are bound
to an io_uring instance. Data is 'read' using a new io_uring request
type. When done, data is returned via a new shared refill queue. A zero
copy page pool refills a hw rx queue from this refill queue directly. Of
course, the lifetime of these data buffers are managed by io_uring
rather than the networking stack, with different refcounting rules.
This patchset is the first step adding basic zero copy support. We will
extend this iteratively with new features e.g. dynamically allocated
zero copy areas, THP support, dmabuf support, improved copy fallback,
general optimisations and more.
In terms of netdev support, we're first targeting Broadcom bnxt. Patches
aren't included since Taehee Yoo has already sent a more comprehensive
patchset adding support in [1]. Google gve should already support this,
and Mellanox mlx5 support is WIP pending driver changes.
===========
Performance
===========
Note: Comparison with epoll + TCP_ZEROCOPY_RECEIVE isn't done yet.
Test setup:
* AMD EPYC 9454
* Broadcom BCM957508 200G
* Kernel v6.11 base [2]
* liburing fork [3]
* kperf fork [4]
* 4K MTU
* Single TCP flow
With application thread + net rx softirq pinned to _different_ cores:
+-------------------------------+
| epoll | io_uring |
|-----------|-------------------|
| 82.2 Gbps | 116.2 Gbps (+41%) |
+-------------------------------+
Pinned to _same_ core:
+-------------------------------+
| epoll | io_uring |
|-----------|-------------------|
| 62.6 Gbps | 80.9 Gbps (+29%) |
+-------------------------------+
=====
Links
=====
Broadcom bnxt support:
[1]: https://lore.kernel.org/netdev/20241003160620.1521626-8-ap420073@xxxxxxxxx/
Linux kernel branch:
[2]: https://github.com/spikeh/linux.git zcrx/v9
liburing for testing:
[3]: https://github.com/isilence/liburing.git zcrx/next
kperf for testing:
[4]: https://git.kernel.dk/kperf.git
We are getting very close to the merge window. In order to get this
series merged before such deadline the point raised by Jakub on this
version must me resolved, the next iteration should land to the ML
before the end of the current working day and the series must apply
cleanly to net-next, so that it can be processed by our CI.
Sounds good, thanks Paolo.
Since the merging is not trivial, I'll send a PR for the net/
patches instead of reposting the entire thing, if that sounds right
to you. The rest will be handled on the io_uring side.
--
Pavel Begunkov
