From: Oleksij Rempel <o.rempel@pengutronix.de>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>,
Pengutronix Kernel Team <kernel@pengutronix.de>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 3/3] drivers/tty: increase priority for tty_buffer_worker
Date: Thu, 10 Jan 2019 16:19:53 +0100 [thread overview]
Message-ID: <20190110151953.qpat4t7lat6plfk6@pengutronix.de> (raw)
In-Reply-To: <CAADWXX_G7X6QkNuqnpMyr+MGP+nUhqPaifJrfC=m57mhJu2jdg@mail.gmail.com>
On Thu, Jan 10, 2019 at 04:54:53AM -0800, Linus Torvalds wrote:
> On Thu, Jan 10, 2019 at 2:12 AM Oleksij Rempel <o.rempel@pengutronix.de> wrote:
> >
> > sched_priority = 1 is enough to dramatically reduce latency
> > on have system load produced by tasks with default user space prio.
>
> .. and is this perhaps a way for a user to then make the system spend
> inordinate amounts of time in the tty layer, and hurting other people?
> I'm thinking threads using pty's etc as a way to make the system
> unresponsive.
>
> We have *never* had good results with random priority modifications.
> People used to do this for the X server, and it helped in very
> specific cases, and hurt enormously in others.
>
> Why would anybody use a tty interface with a l;oopback adapter and
> care about latency?
>
> I can kind of see why you want to do this from a theoretical point,
> but from a *practical* point of view it seems pointless. Why not use
> more appropriate models like networking or pipes etc. IOW, I think you
> should describe what you *really* are doing much more.
>
> "hackbench with a loopback serial adapter" really doesn't sound like
> something that should worry a lot of people.
yes, you right.
> My gut feel is that if somebody still cares deeply about serial line
> latency, they should look at trying to see if they can do some of the
> work directly without the bounce to the workqueue. We use workqueues
> for a reason, but it's possible that some of it could be avoided at
> least in special cases... And yours sounds like a special case.
It is for industrial low latency RS-422 based application. The loopback
test is just easy way to test/reproduce it without additional hardware.
What is good, mainlineable way to implement it?
--
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next prev parent reply other threads:[~2019-01-10 15:19 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-10 10:12 [PATCH v1 0/3] reduce tty latency Oleksij Rempel
2019-01-10 10:12 ` [PATCH v1 1/3] drivers/tty: refactor functions for flushing/queuing work Oleksij Rempel
2019-03-11 8:16 ` Alexander Sverdlin
2019-01-10 10:12 ` [PATCH v1 2/3] drivers/tty: convert tty_port to use kthread_worker Oleksij Rempel
2019-03-11 8:23 ` Alexander Sverdlin
2019-01-10 10:12 ` [PATCH v1 3/3] drivers/tty: increase priority for tty_buffer_worker Oleksij Rempel
2019-01-10 12:54 ` Linus Torvalds
2019-01-10 15:19 ` Oleksij Rempel [this message]
2019-01-10 16:30 ` Greg Kroah-Hartman
2019-01-28 8:05 ` Oleksij Rempel
2019-01-28 8:23 ` Greg Kroah-Hartman
2019-01-28 9:22 ` Oleksij Rempel
2019-01-28 20:03 ` Linus Torvalds
2019-01-28 20:13 ` Linus Torvalds
2019-01-10 16:59 ` Linus Torvalds
2019-03-11 8:24 ` Alexander Sverdlin
2019-01-10 13:51 ` [PATCH v1 0/3] reduce tty latency Greg Kroah-Hartman
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