Date: Fri, 15 Dec 2017 09:05:09 -0600 (CST)
From: Christopher Lameter <cl@linux.com>
To: Peter Zijlstra <peterz@infradead.org>
cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Dave Watson <davejwatson@fb.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-api <linux-api@vger.kernel.org>, Paul Turner <pjt@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Russell King <linux@arm.linux.org.uk>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Andrew Hunter <ahh@google.com>,
        Andi Kleen <andi@firstfloor.org>, Ben Maurer <bmaurer@fb.com>,
        rostedt <rostedt@goodmis.org>, Josh Triplett <josh@joshtriplett.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [RFC PATCH for 4.16 02/21] rseq: Introduce restartable sequences
 system call (v12)
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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.