linux-kernel - Re: [PATCH 7/7] io_uring: add futex waitv

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Message-ID: <20230712093152.GF3100107@hirez.programming.kicks-ass.net>
Date:   Wed, 12 Jul 2023 11:31:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com
Subject: Re: [PATCH 7/7] io_uring: add futex waitv

On Tue, Jul 11, 2023 at 06:47:05PM -0600, Jens Axboe wrote:
> Needs a bit of splitting and a few hunks should go further back (like
> the wake handler typedef).
> 
> WIP, adds IORING_OP_FUTEX_WAITV - pass in an array of futex addresses,
> and wait on all of them until one of them triggers.
> 

So I'm once again not following. FUTEX_WAITV is to wait on multiple
futexes and get a notification when any one of them wakes up with an
index to indicate which one.

How exactly is that different from multiple FUTEX_WAIT entries in the
io_uring thing itself? Admittedly I don't actually know much of anything
when it comes to io_uring, but isn't the idea that queue multiple
'syscall' like things and get individual completions back?

So how does WAITV make sense here?