linux-kernel - Re: [PATCH 0/3] bpf: replace wq users and add WQ_PERCPU to alloc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAADnVQJWCMSbjgV2T+FRLWZ4snjW95arkzNhKKZF6QPcMFDXQA@mail.gmail.com>
Date: Sun, 7 Sep 2025 11:30:29 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Marco Crivellari <marco.crivellari@...e.com>
Cc: LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, 
	Frederic Weisbecker <frederic@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Michal Hocko <mhocko@...e.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH 0/3] bpf: replace wq users and add WQ_PERCPU to
 alloc_workqueue() users

On Fri, Sep 5, 2025 at 1:53 AM Marco Crivellari
<marco.crivellari@...e.com> wrote:
>
> === Plan and future plans ===
>
> This patchset is the first stone on a refactoring needed in order to
> address the points aforementioned; it will have a positive impact also
> on the cpu isolation, in the long term, moving away percpu workqueue in
> favor to an unbound model.
>
> These are the main steps:
> 1)  API refactoring (that this patch is introducing)
>     -   Make more clear and uniform the system wq names, both per-cpu and
>         unbound. This to avoid any possible confusion on what should be
>         used.
>
>     -   Introduction of WQ_PERCPU: this flag is the complement of WQ_UNBOUND,
>         introduced in this patchset and used on all the callers that are not
>         currently using WQ_UNBOUND.
>
>         WQ_UNBOUND will be removed in a future release cycle.
>
>         Most users don't need to be per-cpu, because they don't have
>         locality requirements, because of that, a next future step will be
>         make "unbound" the default behavior.
>
> 2)  Check who really needs to be per-cpu
>     -   Remove the WQ_PERCPU flag when is not strictly required.
>
> 3)  Add a new API (prefer local cpu)
>     -   There are users that don't require a local execution, like mentioned
>         above; despite that, local execution yeld to performance gain.
>
>         This new API will prefer the local execution, without requiring it.
>
> === Introduced Changes by this series ===
>
> 1) [P 1-2] Replace use of system_wq and system_unbound_wq
>
>         system_wq is a per-CPU workqueue, but his name is not clear.
>         system_unbound_wq is to be used when locality is not required.
>
>         Because of that, system_wq has been renamed in system_percpu_wq, and
>         system_unbound_wq has been renamed in system_dfl_wq.
>
> 2) [P 3] add WQ_PERCPU to remaining alloc_workqueue() users
>
>         Every alloc_workqueue() caller should use one among WQ_PERCPU or
>         WQ_UNBOUND. This is actually enforced warning if both or none of them
>         are present at the same time.
>
>         WQ_UNBOUND will be removed in a next release cycle.
>
> === For Maintainers ===
>
> There are prerequisites for this series, already merged in the master branch.

Everything makes sense.

Tejun,
please ack this set just to make sure it's all going as planned.