From: Grant Edwards <grant.b.edwards@gmail.com>
To: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
Subject: Re: locking changes in tty broke low latency feature
Date: Mon, 24 Feb 2014 15:44:59 +0000 (UTC) [thread overview]
Message-ID: <lefpdr$br$1@ger.gmane.org> (raw)
In-Reply-To: alpine.DEB.2.02.1402232330190.21251@ionos.tec.linutronix.de
On 2014-02-23, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Thu, 20 Feb 2014, Peter Hurley wrote:
>> Using Alan's idea to mock up a latency test, I threw together a test
>> jig using two computers running 3.14-rc1 and my fwserial driver
>> (modified to not aggregrate writes) in raw mode where the target does
>> this:
>
> This is a complete pointless test.
No, it isn't. It tested exactly what it was supposed to test: latency
between the driver pushing bytes to the line discipline and user-space
read waking up.
> Use a bog standard 8250 UART on the PC and connect a microcontroller
> on the other end which serves you an continous stream of data at
> 115200 Baud.
>
> There is no way you can keep up with that without the low latency
> option neither on old and nor on new machines if you have enough
> other stuff going on in the system.
That makes no sense. Enabling the low-latency option historically
made it _harder_ to keep up since it caused more overhead in the form
buffer processing and context switches.
--
Grant Edwards grant.b.edwards Yow! Look into my eyes and
at try to forget that you have
gmail.com a Macy's charge card!
next prev parent reply other threads:[~2014-02-24 15:45 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-18 9:38 locking changes in tty broke low latency feature Stanislaw Gruszka
2014-02-18 9:57 ` One Thousand Gnomes
2014-02-18 22:12 ` Peter Hurley
2014-02-19 13:03 ` Stanislaw Gruszka
2014-02-19 16:55 ` Grant Edwards
2014-02-19 17:38 ` Peter Hurley
2014-02-19 18:12 ` Grant Edwards
2014-02-19 18:42 ` Peter Hurley
2014-02-19 19:17 ` One Thousand Gnomes
2014-02-19 20:22 ` Peter Hurley
2014-02-19 21:42 ` One Thousand Gnomes
2014-02-20 2:19 ` Peter Hurley
2014-02-21 15:39 ` One Thousand Gnomes
2014-02-21 15:58 ` Peter Hurley
2014-02-21 16:31 ` Grant Edwards
2014-02-19 23:06 ` Hal Murray
2014-02-19 23:35 ` One Thousand Gnomes
2014-02-20 2:55 ` Peter Hurley
2014-02-20 4:16 ` Greg KH
2014-02-20 18:16 ` Peter Hurley
2014-02-20 19:33 ` Grant Edwards
2014-02-20 22:06 ` Peter Hurley
2014-02-23 22:33 ` Thomas Gleixner
2014-02-24 0:23 ` Peter Hurley
2014-02-24 13:23 ` One Thousand Gnomes
2014-02-24 15:44 ` Grant Edwards [this message]
2014-02-20 21:55 ` Hal Murray
2014-02-20 22:14 ` Grant Edwards
2014-02-21 15:43 ` One Thousand Gnomes
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