Re: [RFC 0/6] implement io_uring notification (ubuf_info) stacking

Pavel Begunkov
2024-04-15T00:08:55Z

On 4/13/24 18:17, David Ahern wrote:
> On 4/12/24 6:55 AM, Pavel Begunkov wrote:
>> io_uring allocates a ubuf_info per zerocopy send request, it's convenient
>> for the userspace but with how things are it means that every time the
>> TCP stack has to allocate a new skb instead of amending into a previous
>> one. Unless sends are big enough, there will be lots of small skbs
>> straining the stack and dipping performance.
>
> The ubuf_info forces TCP segmentation at less than MTU boundaries which
> kills performance with small message sizes as TCP is forced to send
> small packets. This is an interesting solution to allow the byte stream
> to flow yet maintain the segmentation boundaries for callbacks.

Thanks, I'll add your reviews if the patches survive in the
current form!

>> The patchset implements notification, i.e. an io_uring's ubuf_info
>> extension, stacking. It tries to link ubuf_info's into a list, and
>> the entire link will be put down together once all references are
>> gone.
>>
>> Testing with liburing/examples/send-zerocopy and another custom made
>> tool, with 4K bytes per send it improves performance ~6 times and
>> levels it with MSG_ZEROCOPY. Without the patchset it requires much
>> larger sends to utilise all potential.
>>
>> bytes | before | after (Kqps)
>> 100 | 283 | 936
>> 1200 | 195 | 1023
>> 4000 | 193 | 1386
>> 8000 | 154 | 1058
>>
>> Pavel Begunkov (6):
>> net: extend ubuf_info callback to ops structure
>> net: add callback for setting a ubuf_info to skb
>> io_uring/notif: refactor io_tx_ubuf_complete()
>> io_uring/notif: remove ctx var from io_notif_tw_complete
>> io_uring/notif: simplify io_notif_flush()
>> io_uring/notif: implement notification stacking
>>
>> drivers/net/tap.c | 2 +-
>> drivers/net/tun.c | 2 +-
>> drivers/vhost/net.c | 8 +++-
>> include/linux/skbuff.h | 21 ++++++----
>> io_uring/notif.c | 91 +++++++++++++++++++++++++++++++++++-------
>> io_uring/notif.h | 13 +++---
>> net/core/skbuff.c | 37 +++++++++++------
>> 7 files changed, 129 insertions(+), 45 deletions(-)
>>
>

--
Pavel Begunkov