linux-kernel - Re: [PATCH v5 08/24] sched: Introduce per memory space current virtual cpu id

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Date:   Thu, 10 Nov 2022 20:41:07 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        "H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
        linux-api@...r.kernel.org, Christian Brauner <brauner@...nel.org>,
        Florian Weimer <fw@...eb.enyo.de>, David.Laight@...lab.com,
        carlos@...hat.com, Peter Oskolkov <posk@...k.io>,
        Alexander Mikhalitsyn <alexander@...alicyn.com>,
        Chris Kennelly <ckennelly@...gle.com>
Subject: Re: [PATCH v5 08/24] sched: Introduce per memory space current
 virtual cpu id

On Thu, Nov 3, 2022 at 1:05 PM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> This feature allows the scheduler to expose a current virtual cpu id
> to user-space. This virtual cpu id is within the possible cpus range,
> and is temporarily (and uniquely) assigned while threads are actively
> running within a memory space. If a memory space has fewer threads than
> cores, or is limited to run on few cores concurrently through sched
> affinity or cgroup cpusets, the virtual cpu ids will be values close
> to 0, thus allowing efficient use of user-space memory for per-cpu
> data structures.
>

Just to check, is a "memory space" an mm?  I've heard these called
"mms" or sometimes (mostly accurately) "processes" but never memory
spaces.  Although I guess the clone(2) manpage says "memory space".

Also, in my mind "virtual cpu" is vCPU, which this isn't.  Maybe
"compacted cpu" or something?  It's a strange sort of concept.