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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: Wed, 1 Dec 2021 20:29:30 +0000	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 12/1/21 19:59, Pavel Begunkov wrote:
> On 12/1/21 18:10, Willem de Bruijn wrote:
>>> # performance:
>>>
>>> The worst case for io_uring is (4), still 1.88 times faster than
>>> msg_zerocopy (2), and there are a couple of "easy" optimisations left
>>> out from the patchset. For 4096 bytes payload zc is only slightly
>>> outperforms non-zc version, the larger payload the wider gap.
>>> I'll get more numbers next time.
>>
>>> Comparing (3) and (4), and (5) vs (6), @flush doesn't affect it too
>>> much. Notification posting is not a big problem for now, but need
>>> to compare the performance for when io_uring_tx_zerocopy_callback()
>>> is called from IRQ context, and possible rework it to use task_work.
>>>
>>> It supports both, regular buffers and fixed ones, but there is a bunch of
>>> optimisations exclusively for io_uring's fixed buffers. For comparison,
>>> normal vs fixed buffers (@nr_reqs=8, @flush=0): 75677 vs 116079 MB/s
>>>
>>> 1) we pass a bvec, so no page table walks.
>>> 2) zerocopy_sg_from_iter() is just slow, adding a bvec optimised version
>>>     still doing page get/put (see 4/12) slashed 4-5%.
>>> 3) avoiding get_page/put_page in 5/12
>>> 4) completion events are posted into io_uring's CQ, so no
>>>     extra recvmsg for getting events
>>> 5) no poll(2) in the code because of io_uring
>>> 6) lot of time is spent in sock_omalloc()/free allocating ubuf_info.
>>>     io_uring caches the structures reducing it to nearly zero-overhead.
>>
>> Nice set of complementary optimizations.
>>
>> We have looked at adding some of those as independent additions to
>> msg_zerocopy before, such as long-term pinned regions. One issue with
>> that is that the pages must remain until the request completes,
>> regardless of whether the calling process is alive. So it cannot rely
>> on a pinned range held by a process only.
>>
>> If feasible, it would be preferable if the optimizations can be added
>> to msg_zerocopy directly, rather than adding a dependency on io_uring
>> to make use of them. But not sure how feasible that is. For some, like
>> 4 and 5, the answer is clearly it isn't.  6, it probably is?

Forgot about 6), io_uring uses the fact that submissions are
done under an per ring mutex, and completions are under a per
ring spinlock, so there are two lists for them and no extra
locking. Lists are spliced in a batched manner, so it's
1 spinlock per N (e.g. 32) cached ubuf_info's allocations.

Any similar guarantees for sockets?

[...]

-- 
Pavel Begunkov

  reply	other threads:[~2021-12-01 20:30 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 [this message]
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
2021-12-03 16:30             ` Willem de Bruijn

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