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Date:   Mon, 16 Apr 2018 12:26:35 -0700
From:   Linus Torvalds <>
To:     Mathieu Desnoyers <>
Cc:     Andy Lutomirski <>,
        Peter Zijlstra <>,
        "Paul E. McKenney" <>,
        Boqun Feng <>,
        Dave Watson <>,
        linux-kernel <>,
        linux-api <>,
        Paul Turner <>,
        Andrew Morton <>,
        Russell King <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        "H. Peter Anvin" <>, Andrew Hunter <>,
        Andi Kleen <>, Chris Lameter <>,
        Ben Maurer <>, rostedt <>,
        Josh Triplett <>,
        Catalin Marinas <>,
        Will Deacon <>,
        Michael Kerrisk <>
Subject: Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)

On Mon, Apr 16, 2018 at 12:21 PM, Mathieu Desnoyers
<> wrote:
> And I try very hard to avoid being told I'm the one breaking
> user-space. ;-)

You *can't* be breaking user space. User space doesn't use this yet.

That's actually why I'd like to start with the minimal set - to make
sure we don't introduce features that will come back to bite us later.

The one compelling use case I saw was a memory allocator that used
this for getting per-CPU (vs per-thread) memory scaling.

That code didn't need the cpu_opv system call at all.

And if somebody does a ldload of a malloc library, and then wants to
analyze the behavior of a program, maybe they should ldload their own
malloc routines first? That's pretty much par for the course for those
kinds of projects.

So I'd much rather we first merge the non-contentious parts that
actually have some numbers for "this improves performance and makes a
nice fancy malloc possible".

As it is, the cpu_opv seems to be all about theory, not about actual need.


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