linux-kernel - Re: [RFC PATCH for 4.16 02/21] rseq: Introduce restartable sequences system call (v12)

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Message-ID: <alpine.DEB.2.20.1712150903490.14235@nuc-kabylake>
Date:   Fri, 15 Dec 2017 09:05:09 -0600 (CST)
From:   Christopher Lameter <cl@...ux.com>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andrew Hunter <ahh@...gle.com>,
        Andi Kleen <andi@...stfloor.org>, Ben Maurer <bmaurer@...com>,
        rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [RFC PATCH for 4.16 02/21] rseq: Introduce restartable sequences
 system call (v12)

On Thu, 14 Dec 2017, Peter Zijlstra wrote:

> > But my company has extensive user space code that maintains a lot of
> > counters and does other tricks to get full performance out of the
> > hardware. Such a mechanism would also be good from user space. Why keep
> > the good stuff only inside the kernel?
>
> Mathieu's proposal is for userspace, _only_ userspace.

But what we were talking about are instructions that work effectively in
kernel space whose efficiency restartable sequences could bring to user
space.