linux-kernel - Re: [RFC PATCH for 4.18 00/14] Restartable Sequences

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Message-ID: <CAKOZuetW5NEvbROjuquQ_AxrW7BqR5Qfp6BYfy+zUrnPkZDaTw@mail.gmail.com>
Date:   Thu, 03 May 2018 16:22:00 +0000
From:   Daniel Colascione <dancol@...gle.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        boqun.feng@...il.com, luto@...capital.net, davejwatson@...com,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux@....linux.org.uk, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, Andrew Hunter <ahh@...gle.com>, andi@...stfloor.org,
        cl@...ux.com, bmaurer@...com, rostedt@...dmis.org,
        josh@...htriplett.org, torvalds@...ux-foundation.org,
        catalin.marinas@....com, will.deacon@....com,
        Michael Kerrisk-manpages <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [RFC PATCH for 4.18 00/14] Restartable Sequences

On Thu, May 3, 2018 at 9:12 AM Mathieu Desnoyers <
mathieu.desnoyers@...icios.com> wrote:
> By the way, if we eventually find a way to enhance user-space mutexes in
the
> fashion you describe here, it would belong to another TLS area, and would
> be registered by another system call than rseq. I proposed a more generic
> "TLS area registration" system call a few years ago, but Linus told me he
> wanted a system call that was specific to rseq. If we need to implement
> other use-cases in a TLS area shared between kernel and user-space in a
> similar fashion, the plan is to do it in a distinct system call.

If we proliferate TLS areas; we'd have to register each one upon thread
creation, adding to the overall thread creation path. There's already a
provision for versioning the TLS area. What's the benefit of splitting the
registration over multiple system calls?