linux-kernel - Re: [RFC PATCH 0/2] RT scheduling policies for workqueues

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Message-ID: <20220328180739.o2nka5u72jj66ipg@pengutronix.de>
Date:   Mon, 28 Mar 2022 20:07:39 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Tejun Heo <tj@...nel.org>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Peter Hurley <peter@...leysoftware.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Esben Haabendal <esben@...nix.com>,
        Steven Walter <stevenrwalter@...il.com>,
        linux-kernel@...r.kernel.org,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        André Pribil <a.pribil@...k-ipc.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-rt-users@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] RT scheduling policies for workqueues

On 28.03.2022 07:39:25, Tejun Heo wrote:
> Hello,
> 
> On Mon, Mar 28, 2022 at 12:09:27PM +0200, Marc Kleine-Budde wrote:
> > > Having a kthread per "low-latency" tty instance is something I would
> > > prefer. The kwork corner is an anonymous worker instance and probably
> > > does more harm than good. Especially if it is a knob for everyone which
> > > is used for the wrong reasons and manages to be harmful in the end.
> > > With a special kthread for a particular tty, the thread can be assigned
> > > with the desired priority within the system and ttyS1 can be
> > > distinguished from ttyS0 (and so on). This turned out to be useful in a
> > > few setups over the years.
> > 
> > +1
> > 
> > The networking subsystem has gone the same/similar way with NAPI. NAPI
> > handling can be switched from the softirq to kernel thread on a per
> > interface basis.
> 
> I wonder whether it'd be useful to provide a set of wrappers which can make
> switching between workqueue and kworker easy. Semantics-wise, they're
> already mostly aligned and it shouldn't be too difficult to e.g. make an
> unbounded workqueue be backed by a dedicated kthread_worker instead of
> shared pool depending on a flag, or even allow switching dynamically.

For NAPI a sysfs entry was added to switch to threaded mode:

| 5fdd2f0e5c64 net: add sysfs attribute to control napi threaded mode
| 29863d41bb6e net: implement threaded-able napi poll loop support
| 898f8015ffe7 net: extract napi poll functionality to __napi_poll()

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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