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.2.20.1712141512360.8945@nuc-kabylake>
Date:   Thu, 14 Dec 2017 15:14:00 -0600 (CST)
From:   Christopher Lameter <cl@...ux.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        "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, Mathieu Desnoyers wrote:

> If we port this concept to kernel-space (as I start to understand
> would be your wish), then a simple pointer store to the current
> task_struct would suffice.

Certainly such a port would be beneficial for non x86 archs.

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?