linux-kernel - Re: [PATCHSET v3 0/5] Add support for epoll min

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Date:   Sat, 5 Nov 2022 11:39:14 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCHSET v3 0/5] Add support for epoll min_wait

>> FWIW, when adding nsec resolution I initially opted for an init-based
>> approach, passing a new flag to epoll_create1. Feedback then was that
>> it was odd to have one syscall affect the behavior of another. The
>> final version just added a new epoll_pwait2 with timespec.
> 
> I'm fine with just doing a pure syscall variant too, it was my original
> plan. Only changed it to allow for easier experimentation and adoption,
> and based on the fact that most use cases would likely use a fixed value
> per context anyway.
> 
> I think it'd be a shame to drop the ctl, unless there's strong arguments
> against it. I'm quite happy to add a syscall variant too, that's not a
> big deal and would be a minor addition. Patch 6 should probably cut out
> the ctl addition and leave that for a patch 7, and then a patch 8 for
> adding a syscall.
I split the ctl patch out from the core change, and then took a look at
doing a syscall variant too. But there are a few complications there...
It would seem to make the most sense to build this on top of the newest
epoll wait syscall, epoll_pwait2(). But we're already at the max number
of arguments there...

Arguably pwait2 should've been converted to use some kind of versioned
struct instead. I'm going to take a stab at pwait3 with that kind of
interface.

-- 
Jens Axboe