linux-kernel - Re: [PATCH v3 0/4] fast poll multishot mode

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Date:   Sat, 7 May 2022 09:28:58 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Hao Xu <haoxu.linux@...il.com>, io-uring@...r.kernel.org
Cc:     Pavel Begunkov <asml.silence@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/4] fast poll multishot mode

On 5/7/22 8:06 AM, Hao Xu wrote:
> Let multishot support multishot mode, currently only add accept as its
> first comsumer.

consumer

> theoretical analysis:
>   1) when connections come in fast
>     - singleshot:
>               add accept sqe(userpsace) --> accept inline

userspace

>                               ^                 |
>                               |-----------------|
>     - multishot:
>              add accept sqe(userspace) --> accept inline
>                                               ^     |
>                                               |--*--|
> 
>     we do accept repeatedly in * place until get EAGAIN
> 
>   2) when connections come in at a low pressure
>     similar thing like 1), we reduce a lot of userspace-kernel context
>     switch and useless vfs_poll()

Overall this looks better than v2 for sure, just some minor tweaks
needed I believe.

But we still need to consider direct accept with multishot... Should
probably be an add-on patch as I think it'd get a bit more complicated
if we need to be able to cheaply find an available free fixed fd slot.
I'll try and play with that.

-- 
Jens Axboe