Re: [PATCH] serial: imx: reduce RX interrupt frequency - Marc Kleine-Budde

From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Tomasz Moń" <tomasz.mon@camlingroup.com>,
	"Pengutronix Kernel Team" <kernel@pengutronix.de>,
	"Jiri Slaby" <jirislaby@kernel.org>,
	"Sascha Hauer" <s.hauer@pengutronix.de>,
	"NXP Linux Team" <linux-imx@nxp.com>,
	linux-serial@vger.kernel.org,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Shawn Guo" <shawnguo@kernel.org>,
	"Fabio Estevam" <festevam@gmail.com>,
	k.drobinski@camlintechnologies.com
Subject: Re: [PATCH] serial: imx: reduce RX interrupt frequency
Date: Wed, 5 Jan 2022 11:57:02 +0100	[thread overview]
Message-ID: <20220105105702.vrz7u3nam27izwah@pengutronix.de> (raw)
In-Reply-To: <YdV00WYGGd49WYt9@kroah.com>

[-- Attachment #1: Type: text/plain, Size: 1841 bytes --]

On 05.01.2022 11:37:05, Greg Kroah-Hartman wrote:
> On Wed, Jan 05, 2022 at 08:59:09AM +0100, Tomasz Moń wrote:
> > On 04.01.2022 23:49, Uwe Kleine-König wrote:
> > > On Tue, Jan 04, 2022 at 12:38:01PM +0100, Greg Kroah-Hartman wrote:
> > >> On Tue, Jan 04, 2022 at 12:13:06PM +0100, Tomasz Moń wrote:
> > >>> On 04.01.2022 11:54, Greg Kroah-Hartman wrote:
> > >>>> Why can't you do this dynamically based on the baud rate so as to always
> > >>>> work properly for all speeds without increased delays for slower ones?
> > >>>
> > >>> Could you please advise on which baud rates to consider as slow? Does it
> > >>> sound good to have the old trigger level for rates up to and including
> > >>> 115200 and the new one for faster ones?
> > >>
> > >> You tell me, you are the one seeing this issue and are seeing delays on
> > >> slower values with your change.  Do some testing to see where the curve
> > >> is.
> > 
> > While the increased latency due to this change is undeniable, it is
> > important to note that latency is not everything. There are applications
> > where the latency is crucial, however using Linux for such applications
> > is questionable. Linux is not a Real Time Operating System after all.
> 
> Yes, Linux can be used in real time situtations just fine, look at the
> RT patchset for proof of that.
> 
> So let's not make things any worse for no good reason if at all
> possible.

+1

We have a $CUSTOMER, where serial latency is crucial. And we have a task
to cut down latencies and jitter even more.

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 |

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]