linux-kernel - Re: 'simple' futex interface [Was: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes]

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Message-ID: <87imji7or0.fsf@oldenburg2.str.redhat.com>
Date:   Thu, 05 Mar 2020 17:25:23 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     André Almeida <andrealmeid@...labora.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Pierre-Loup A. Griffais" <pgriffais@...vesoftware.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, kernel@...labora.com,
        krisman@...labora.com, shuah@...nel.org,
        linux-kselftest@...r.kernel.org, rostedt@...dmis.org,
        ryao@...too.org, dvhart@...radead.org, mingo@...hat.com,
        z.figura12@...il.com, steven@...vesoftware.com,
        steven@...uorix.net, malteskarupke@....de, carlos@...hat.com,
        adhemerval.zanella@...aro.org, libc-alpha@...rceware.org,
        linux-api@...r.kernel.org
Subject: Re: 'simple' futex interface [Was: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes]

* André Almeida:

> Thanks everyone for the feedback around our mechanism. Are the
> performance benefits of implementing a syscall to wait on a single futex
> significant enough to maintain it instead of just using
> `sys_futex_waitv()` with `nr_waiters = 1`? If we join both cases in a
> single interface, we may even add a new member for NUMA hint in `struct
> futex_wait`.

Some seccomp user might want to verify the address, and that's easier if
it's in an argument.  But that's just a rather minor aspect.

Do you propose to drop the storage requirement for the NUMA hint
next to the futex completely?

Thanks,
Florian