Re: [PATCH net-next v4 00/27] io_uring zerocopy send

[David Ahern <dsahern@kernel.org>]

On 7/7/22 5:49 AM, Pavel Begunkov wrote:
> NOTE: Not be picked directly. After getting necessary acks, I'll be working
>       out merging with Jakub and Jens.
> 
> The patchset implements io_uring zerocopy send. It works with both registered
> and normal buffers, mixing is allowed but not recommended. Apart from usual
> request completions, just as with MSG_ZEROCOPY, io_uring separately notifies
> the userspace when buffers are freed and can be reused (see API design below),
> which is delivered into io_uring's Completion Queue. Those "buffer-free"
> notifications are not necessarily per request, but the userspace has control
> over it and should explicitly attaching a number of requests to a single
> notification. The series also adds some internal optimisations when used with
> registered buffers like removing page referencing.
> 
> From the kernel networking perspective there are two main changes. The first
> one is passing ubuf_info into the network layer from io_uring (inside of an
> in kernel struct msghdr). This allows extra optimisations, e.g. ubuf_info
> caching on the io_uring side, but also helps to avoid cross-referencing
> and synchronisation problems. The second part is an optional optimisation
> removing page referencing for requests with registered buffers.
> 
> Benchmarking with an optimised version of the selftest (see [1]), which sends
> a bunch of requests, waits for completions and repeats. "+ flush" column posts
> one additional "buffer-free" notification per request, and just "zc" doesn't
> post buffer notifications at all.
> 
> NIC (requests / second):
> IO size | non-zc    | zc             | zc + flush
> 4000    | 495134    | 606420 (+22%)  | 558971 (+12%)
> 1500    | 551808    | 577116 (+4.5%) | 565803 (+2.5%)
> 1000    | 584677    | 592088 (+1.2%) | 560885 (-4%)
> 600     | 596292    | 598550 (+0.4%) | 555366 (-6.7%)
> 
> dummy (requests / second):
> IO size | non-zc    | zc             | zc + flush
> 8000    | 1299916   | 2396600 (+84%) | 2224219 (+71%)
> 4000    | 1869230   | 2344146 (+25%) | 2170069 (+16%)
> 1200    | 2071617   | 2361960 (+14%) | 2203052 (+6%)
> 600     | 2106794   | 2381527 (+13%) | 2195295 (+4%)
> 
> Previously it also brought a massive performance speedup compared to the
> msg_zerocopy tool (see [3]), which is probably not super interesting.
> 

can you add a comment that the above results are for UDP.

You dropped comments about TCP testing; any progress there? If not, can
you relay any issues you are hitting?