netdev - RE: [PATCH] net: add support for threaded NAPI polling

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Message-ID: <1743bcaa2dfb4b6393b4d228cf079fe3@AcuMS.aculab.com>
Date:   Thu, 30 Jul 2020 15:42:49 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Sebastian Gottschall' <s.gottschall@...wrt.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Felix Fietkau <nbd@....name>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Hillf Danton <hdanton@...a.com>
Subject: RE: [PATCH] net: add support for threaded NAPI polling

From: Sebastian Gottschall
> Sent: 30 July 2020 15:30
...
> > Quite frankly, I do believe this STATE_THREADED status should be a generic NAPI attribute
> > that can be changed dynamically, at admin request, instead of having to change/recompile
> > a driver.

> thats not that easy. wifi devices do use dummy netdev devices. they are
> not visible to sysfs and other administrative options.
> so changing it would just be possible if a special mac80211 based
> control would be implemented for these drivers.
> for standard netdev devices it isnt a big thing to implement a
> administrative control by sysfs (if you are talking about such a feature)

ISTM that a global flag that made all NAPI callbacks be made
from a worker thread rather than softint would be more approriate.
Or even something that made the softint callbacks themselves
only run an a specific high(ish) priority kernel thread.

While it might slow down setups that need very low ethernet
latency it will help those that don't want application RT threads
to be 'stolen' by the softint code while they hold application
mutex or are waiting to be woken by a cv.

	David

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