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From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "André Almeida" <andrealmeid@collabora.com>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Darren Hart" <dvhart@infradead.org>,
	linux-kernel@vger.kernel.org,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
	kernel@collabora.com, krisman@collabora.com,
	linux-api@vger.kernel.org, libc-alpha@sourceware.org,
	mtk.manpages@gmail.com, "Davidlohr Bueso" <dave@stgolabs.net>
Subject: Re: [PATCH 2/4] futex2: Implement vectorized wait
Date: Wed, 18 Aug 2021 18:20:34 +0200	[thread overview]
Message-ID: <20210818162034.GA26408@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <87v94310gm.ffs@tglx>

On Wed, Aug 18, 2021 at 01:00:57PM +0200, Thomas Gleixner wrote:
> > +/**
> > + * struct futex_waitv - A waiter for vectorized wait
> > + * @val:   Expected value at uaddr
> > + * @uaddr: User address to wait on
> > + * @flags: Flags for this waiter
> > + */
> > +struct futex_waitv {
> > +	__u64 val;
> 
> Again. Why u64?

So I think the idea was that if we're going to do new syscalls, we
should cater for future extentions, one of which was 64bit futexes (for
64bit archs) (along with u{8,16,32})

The previous set of patches implemented a more complete replacement ABI
-- which I rather liked, however the implementation was completely
disjoint from the existing futexes, which was a non-starter for me.

Anyway, yes, current futexes are u32, but if we want to ever do u64
futexes, we should either do this syscall with a u64, or already plan to
retire the whole syscall.

Obiously this would've made good Changelog material, but alas it wasn't
there.


  reply	other threads:[~2021-08-18 16:22 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-05 19:04 [PATCH 0/4] futex2: Add wait on multiple futexes syscall André Almeida
2021-08-05 19:04 ` [PATCH 1/4] futex: Prepare for futex_wait_multiple() André Almeida
2021-08-18  8:22   ` Thomas Gleixner
2021-08-05 19:04 ` [PATCH 2/4] futex2: Implement vectorized wait André Almeida
2021-08-18 11:00   ` Thomas Gleixner
2021-08-18 16:20     ` Peter Zijlstra [this message]
2021-08-18 16:34       ` André Almeida
2021-08-18 19:45       ` Thomas Gleixner
2021-08-19  3:38         ` André Almeida
2021-08-05 19:04 ` [PATCH 3/4] selftests: futex2: Add waitv test André Almeida
2021-08-05 19:04 ` [PATCH 4/4] futex2: Documentation: Document futex_waitv() uAPI André Almeida

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