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References: <20221103200359.328736-1-mathieu.desnoyers@efficios.com> <20221103200359.328736-9-mathieu.desnoyers@efficios.com>
In-Reply-To: <20221103200359.328736-9-mathieu.desnoyers@efficios.com>
From:   Andy Lutomirski <luto@amacapital.net>
Date:   Thu, 10 Nov 2022 20:41:07 -0800
Message-ID: <CALCETrW1doHX3=za+KDuB=4y+wHsnaZpVkDP3OhZXGrQU2iffw@mail.gmail.com>
Subject: Re: [PATCH v5 08/24] sched: Introduce per memory space current
 virtual cpu id
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        "H . Peter Anvin" <hpa@zytor.com>, Paul Turner <pjt@google.com>,
        linux-api@vger.kernel.org, Christian Brauner <brauner@kernel.org>,
        Florian Weimer <fw@deneb.enyo.de>, David.Laight@aculab.com,
        carlos@redhat.com, Peter Oskolkov <posk@posk.io>,
        Alexander Mikhalitsyn <alexander@mihalicyn.com>,
        Chris Kennelly <ckennelly@google.com>
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On Thu, Nov 3, 2022 at 1:05 PM Mathieu Desnoyers
<mathieu.desnoyers@efficios.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.