From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Jiri Pirko <jiri@resnulli.us>,
netdev@vger.kernel.org, Dave Taht <dave.taht@gmail.com>,
Jamal Hadi Salim <jhs@mojatatu.com>,
kernel@pengutronix.de, Cong Wang <xiyou.wangcong@gmail.com>,
linux-can@vger.kernel.org, davem@davemloft.net
Subject: Re: [RFC] net: sch_generic: fq_codel vs pfifo_fast
Date: Wed, 27 Mar 2019 20:24:13 +0100 [thread overview]
Message-ID: <0edf15df-b607-70f7-5fe8-2860eb663a53@pengutronix.de> (raw)
In-Reply-To: <20190327113059.6b1224ab@shemminger-XPS-13-9360>
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On 3/27/19 7:30 PM, Stephen Hemminger wrote:
>> on CAN networking hardware we (the CAN community) experience a lot silent,
>> unwanted frame drops inside the kernel. (See first patch for details.) So
>> here's a patch series to keep pfifo_fast as default scheduler for CAN hardware
>> by default.
>
> Why do you set fq_codel as default qdisc if you know it doesn't work right for your
> environment. Is this a distro's want one value problem?
This is a many fold problem.
- Consider a random Linux developer attaching one of the mainline
supported USB-CAN adapters to his/her development laptop and doing some
random CAN test. As far a I heard all modern Linux distributions (but
not debian) enable fq_codel per kernel .config or via systemd. The user
will experiences dropped CAN frames on the first 1000 packages. This is
not a good user experience.
- From the user space point of view the sysctl net.core.default_qdisc
behaves a bit strange. Why can I enable a queuing discipline by default
that's known not to work on CAN devices. You might think the kernel
(should) know that CAN devices best work with pfifo_fast (or not
NET_SCHED at all).
- Addressing your question directly: Mixed environment. fq_codel works
great on Ethernet, but terrible on CAN. Of course I an use "tc" to
configure the way I want to. But from my point of view it would be nice,
if the kernel uses sane default...and handles the net.core.default_qdisc
default in a sane way.
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Industrial Linux Solutions | Phone: +49-231-2826-924 |
Vertretung West/Dortmund | Fax: +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
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next prev parent reply other threads:[~2019-03-27 19:24 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-27 16:56 [RFC] net: sch_generic: fq_codel vs pfifo_fast Marc Kleine-Budde
2019-03-27 16:56 ` [PATCH 1/2] net: sch_generic: add flag IFF_FIFO_QUEUE to use pfifo_fast as default scheduler Marc Kleine-Budde
2019-03-27 17:14 ` Cong Wang
2019-03-27 20:11 ` Marc Kleine-Budde
2019-03-27 20:53 ` Cong Wang
2019-04-02 17:22 ` Toke Høiland-Jørgensen
2019-03-27 18:53 ` Uwe Kleine-König
2019-03-27 19:27 ` Marc Kleine-Budde
2019-03-27 16:56 ` [PATCH 2/2] can: dev: let all CAN devices " Marc Kleine-Budde
2019-03-27 18:30 ` [RFC] net: sch_generic: fq_codel vs pfifo_fast Stephen Hemminger
2019-03-27 19:24 ` Marc Kleine-Budde [this message]
2019-10-22 12:47 ` [PATCH] net: sch_generic: Use pfifo_fast as fallback scheduler for CAN hardware Vincent Prince
2019-10-22 12:58 ` Marc Kleine-Budde
2019-10-22 13:23 ` [PATCH v2] " Vincent Prince
2019-10-22 14:53 ` Marc Kleine-Budde
2019-10-22 14:55 ` Marc Kleine-Budde
2019-10-22 16:42 ` Stephen Hemminger
2019-10-22 16:48 ` Marc Kleine-Budde
2019-10-22 17:28 ` Eric Dumazet
2019-10-22 18:21 ` Oliver Hartkopp
2019-10-22 15:09 ` [PATCH v3] " Vincent Prince
2019-10-23 10:52 ` [PATCH v4] " Vincent Prince
2019-10-23 11:13 ` Dave Taht
2019-10-23 13:44 ` [PATCH v5] " Vincent Prince
2019-10-26 2:20 ` David Miller
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