linux-kernel - Re: [RFC PATCH 03/13] futex2: Implement vectorized wait

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Message-ID: <87ft1xw123.fsf@collabora.com>
Date:   Mon, 15 Feb 2021 15:03:48 -0500
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     André Almeida <andrealmeid@...labora.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        kernel@...labora.com, pgriffais@...vesoftware.com,
        z.figura12@...il.com, joel@...lfernandes.org,
        malteskarupke@...tmail.fm, linux-api@...r.kernel.org,
        fweimer@...hat.com, libc-alpha@...rceware.org,
        linux-kselftest@...r.kernel.org, shuah@...nel.org, acme@...nel.org,
        corbet@....net
Subject: Re: [RFC PATCH 03/13] futex2: Implement vectorized wait

André Almeida <andrealmeid@...labora.com> writes:

> Add support to wait on multiple futexes. This is the interface
> implemented by this syscall:
>
> futex_waitv(struct futex_waitv *waiters, unsigned int nr_futexes,
> 	    unsigned int flags, struct timespec *timo)
>
> struct futex_waitv {
> 	void *uaddr;
> 	unsigned int val;
> 	unsigned int flags;
> };
>
> Given an array of struct futex_waitv, wait on each uaddr. The thread
> wakes if a futex_wake() is performed at any uaddr. The syscall returns
> immediately if any waiter has *uaddr != val. *timo is an optional
> timeout value for the operation. The flags argument of the syscall
> should be used solely for specifying the timeout as realtime, if needed.
> Flags for shared futexes, sizes, etc. should be used on the individual
> flags of each waiter.

Given the previous proposal from Zebediah, one use case Wine has to
support is the ability to wait on all (instead of any) of a list of
futexes .  I suppose that could be done by a new FLAG_WAITALL passed on
the third argument of the syscall.

-- 
Gabriel Krisman Bertazi