linux-kernel - Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu

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Message-ID: <CA+55aFxcJ2V_1BoW0Cct=Kkp7REkgiU_BTimGdmoFmWHaWaZ-g@mail.gmail.com>
Date:   Thu, 12 Apr 2018 12:43:27 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
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 Mailing List <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>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)

On Thu, Apr 12, 2018 at 12:27 PM, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
> The cpu_opv system call executes a vector of operations on behalf of
> user-space on a specific CPU with preemption disabled. It is inspired
> by readv() and writev() system calls which take a "struct iovec"
> array as argument.

Do we really want the page pinning?

This whole cpu_opv thing is the most questionable part of the series,
and the page pinning is the most questionable part of cpu_opv for me.

Can we plan on merging just the plain rseq parts *without* this all
first, and then see the cpu_opv thing as a "maybe future expansion"
part.

I think that would make Andy happier too.

             Linus