netdev - Re: [PATCH net-next v4 00/27] io

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Date:   Fri, 8 Jul 2022 15:26:13 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     David Ahern <dsahern@...nel.org>, io-uring@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jens Axboe <axboe@...nel.dk>, kernel-team@...com
Subject: Re: [PATCH net-next v4 00/27] io_uring zerocopy send

On 7/8/22 05:10, David Ahern wrote:
> 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.

Oh, right, forgot to add it


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

Not really a problem, but for me it's bottle necked at NIC bandwidth
(~3GB/s) for both zc and non-zc and doesn't even nearly saturate a CPU.
Was actually benchmarked by my colleague quite a while ago, but can't
find numbers. Probably need to at least add localhost numbers or grab
a better server.

-- 
Pavel Begunkov