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From: Pavel Begunkov <[email protected]>
To: Willem de Bruijn <[email protected]>
Cc: [email protected], [email protected],
	[email protected], Jakub Kicinski <[email protected]>,
	Jonathan Lemon <[email protected]>,
	"David S . Miller" <[email protected]>,
	Eric Dumazet <[email protected]>,
	Hideaki YOSHIFUJI <[email protected]>,
	David Ahern <[email protected]>, Jens Axboe <[email protected]>
Subject: Re: [RFC 00/12] io_uring zerocopy send
Date: Fri, 3 Dec 2021 16:19:28 +0000	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+FuTSfe63=SuuZeC=eZPLWstgOL6oFUrsL4o+J8=3BwHJSTVg@mail.gmail.com>

On 12/2/21 21:25, Willem de Bruijn wrote:
>>> What if the ubuf pool can be found from the sk, and the index in that
>>> pool is passed as a cmsg?
>>
>> It looks to me that ubufs are by nature is something that is not
>> tightly bound to a socket (at least for io_uring API in the patchset),
>> it'll be pretty ugly:
>>
>> 1) io_uring'd need to care to register the pool in the socket. Having
>> multiple rings using the same socket would be horrible. It may be that
>> it doesn't make much sense to send in parallel from multiple rings, but
>> a per thread io_uring is a popular solution, and then someone would
>> want to pass a socket from one thread to another and we'd need to support
>> it.
>>
>> 2) And io_uring would also need to unregister it, so the pool would
>> store a list of sockets where it's used, and so referencing sockets
>> and then we need to bind it somehow to io_uring fixed files or
>> register all that for tracking referencing circular dependencies.
>>
>> 3) IIRC, we can't add a cmsg entry from the kernel, right? May be wrong,
>> but if so I don't like exposing basically io_uring's referencing through
>> cmsg. And it sounds io_uring would need to parse cmsg then.
>>
>>
>> A lot of nuances :) I'd really prefer to pass it on per-request basis,
> 
> Ok
> 
>> it's much cleaner, but still haven't got what's up with msghdr
>> initialisation...
> 
> And passing the struct through multiple layers of functions.

If you refer to ip_make_skb(ubuf) -> __ip_append_data(ubuf), I agree
it's a bit messier, will see what can be done. If you're about
msghdr::msg_ubuf, for me it's more like passing a callback,
which sounds like a normal thing to do.


>> Maybe, it's better to add a flags field, which would include
>> "msg_control_is_user : 1" and whether msghdr includes msg_iocb, msg_ubuf,
>> and everything else that may be optional. Does it sound sane?
> 
> If sendmsg takes the argument, it will just have to be initialized, I think.
> 
> Other functions are not aware of its existence so it can remain
> uninitialized there.

Got it, need to double check, but looks something like 1/12 should
be as you outlined.

And if there will be multiple optional fields that have to be
initialised, we would be able to hide all the zeroing under a
single bitmask. E.g. instead of

msg->field1 = NULL;
...
msg->fieldN = NULL;

It may look like

msg->mask = 0; // HAS_FIELD1 | HAS_FIELDN;

-- 
Pavel Begunkov

  reply	other threads:[~2021-12-03 16:19 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-30 15:18 [RFC 00/12] io_uring zerocopy send Pavel Begunkov
2021-11-30 15:18 ` [RFC 01/12] skbuff: add SKBFL_DONT_ORPHAN flag Pavel Begunkov
2021-11-30 15:18 ` [RFC 02/12] skbuff: pass a struct ubuf_info in msghdr Pavel Begunkov
2021-11-30 15:18 ` [RFC 03/12] net/udp: add support msgdr::msg_ubuf Pavel Begunkov
2021-11-30 15:18 ` [RFC 04/12] net: add zerocopy_sg_from_iter for bvec Pavel Begunkov
2021-11-30 15:18 ` [RFC 05/12] net: optimise page get/free for bvec zc Pavel Begunkov
2021-12-01 19:20   ` Jonathan Lemon
2021-12-01 20:17     ` Pavel Begunkov
2021-11-30 15:18 ` [RFC 06/12] io_uring: add send notifiers registration Pavel Begunkov
2021-11-30 15:18 ` [RFC 07/12] io_uring: infrastructure for send zc notifications Pavel Begunkov
2021-11-30 15:18 ` [RFC 08/12] io_uring: wire send zc request type Pavel Begunkov
2021-11-30 15:18 ` [RFC 09/12] io_uring: add an option to flush zc notifications Pavel Begunkov
2021-11-30 15:18 ` [RFC 10/12] io_uring: opcode independent fixed buf import Pavel Begunkov
2021-11-30 15:18 ` [RFC 11/12] io_uring: sendzc with fixed buffers Pavel Begunkov
2021-11-30 15:19 ` [RFC 12/12] io_uring: cache struct ubuf_info Pavel Begunkov
2021-12-01  3:10 ` [RFC 00/12] io_uring zerocopy send David Ahern
2021-12-01 15:32   ` Pavel Begunkov
2021-12-01 17:57     ` David Ahern
     [not found]       ` <[email protected]>
2021-12-01 19:20         ` David Ahern
2021-12-01 20:15           ` Pavel Begunkov
2021-12-01 21:51             ` Martin KaFai Lau
2021-12-01 22:35               ` David Ahern
2021-12-01 23:07                 ` Martin KaFai Lau
2021-12-01 23:18                   ` Pavel Begunkov
2021-12-02 15:48               ` Pavel Begunkov
2021-12-02 17:40                 ` Martin KaFai Lau
2021-12-01 20:42       ` Pavel Begunkov
2021-12-01 14:31 ` Pavel Begunkov
2021-12-01 17:49   ` David Ahern
2021-12-01 19:59     ` Pavel Begunkov
2021-12-01 18:10 ` Willem de Bruijn
2021-12-01 19:59   ` Pavel Begunkov
2021-12-01 20:29     ` Pavel Begunkov
2021-12-02  0:36       ` Willem de Bruijn
2021-12-02 16:25         ` Pavel Begunkov
2021-12-02  0:32     ` Willem de Bruijn
2021-12-02 16:45       ` Pavel Begunkov
2021-12-02 21:25         ` Willem de Bruijn
2021-12-03 16:19           ` Pavel Begunkov [this message]
2021-12-03 16:30             ` Willem de Bruijn

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