From: Theodore Tso <tytso@mit.edu>
To: Geir Thomassen <geirt@powertech.no>
Cc: Theodore Tso <tytso@mit.edu>, linux-kernel@vger.kernel.org
Subject: Re: Serial port latency
Date: Thu, 22 Mar 2001 16:44:57 -0600 [thread overview]
Message-ID: <20010322164457.A4886@think> (raw)
In-Reply-To: <3ABA42A8.A806D0E7@powertech.no> <20010322140852.A4110@think> <3ABA6167.309E6DB2@powertech.no>
In-Reply-To: <3ABA6167.309E6DB2@powertech.no>; from geirt@powertech.no on Thu, Mar 22, 2001 at 09:32:39PM +0100
On Thu, Mar 22, 2001 at 09:32:39PM +0100, Geir Thomassen wrote:
>
> The serial port chip is 16550A, which has a built in fifo. Can this be
> the source of my problems ?
Well, if you set the uart to be 16450 using setserial, this will cause
Linux to avoid enabling the FIFO. That will cause the loop to save
the 4 character times (which at 9600 bps is 4ms). If your original
protocol is writing six characters, and then reads 2 characters in a
tight loop, that means a total cycle takes 8ms, and disabling the FIFO
will have significant savings assuming that all other causes of
latencies have been removed. (The FIFO delay can cause a slowdown by
50%).
- Ted
next prev parent reply other threads:[~2001-03-22 22:46 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-03-22 18:21 Serial port latency Geir Thomassen
2001-03-22 20:08 ` Theodore Tso
2001-03-22 20:32 ` Geir Thomassen
2001-03-22 20:55 ` Paul Fulghum
2001-03-22 22:44 ` Theodore Tso [this message]
[not found] ` <20010322141937.C22479@universal-fasteners.com>
2001-03-22 21:02 ` Geir Thomassen
2001-03-22 21:52 ` Jonathan Lundell
2001-03-22 23:25 ` Pavel Machek
2001-03-23 14:43 ` Geir Thomassen
[not found] <Pine.LNX.4.20.0103221219410.3343-100000@linuxtaj.korpivaara.org>
2001-03-22 20:03 ` Geir Thomassen
2001-03-22 20:17 ` Trent Jarvi
-- strict thread matches above, loose matches on Subject: below --
2001-03-22 21:45 Manfred Spraul
[not found] <000401c0b319517fea9@local>
2001-03-25 23:10 ` Pavel Machek
2001-03-29 7:58 ` Manfred Spraul
2001-03-30 22:36 ` Pavel Machek
2001-03-31 22:09 ` Manfred Spraul
2001-04-10 0:37 ` Andrea Arcangeli
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