linux-kernel - Re: Linux Serial Performance

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Message-ID: <m363793jg1.fsf@intrepid.localdomain>
Date:	Sun, 10 Jan 2010 19:26:22 +0100
From:	Krzysztof Halasa <khc@...waw.pl>
To:	"Paul G. Allen" <pgallen@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Linux Serial Performance

"Paul G. Allen" <pgallen@...il.com> writes:

> I ran some tests on Windows XP and Linux CentOS 5.1 using the Sun
> NetBeans IDE 6.7.1 profiler. The same Java code on both Linux and XP
> machines, the same model of machine (Dell, Pentium 4 3GHz, 2.5GB
> memory). I am using the Sun comm API currently, and previously I was
> using the Serlio API. In all cases, the profiler shows the serial Tx
> to be about 20x faster (twenty times) on Windows XP than in Linux. It
> takes Linux several seconds to Tx 1024 byte blocks of data over the
> serial port where Windows XP takes a fraction of a second.

I don't know about Java, but I'm using 460 kb/s and 920 kb/s serial
ports and Linux can transmit (and receive) full speed data without any
problem. This includes mobile Pentium III 500 MHz with 460 kb/s NS super
IO chip.

4-port OX16PCI954, PL2303 (max 2) and FTDI2232-based USB dongles also
work as well. I know people use ca. 4 Mb/s async serial (with PPP).

The last time I remember serial IO problems it was 8-port 8251-based ISA
card on 486DX. I think it was reliable at max 19200 b/s.

Perhaps you're requesting hardware (or software) handshaking when it's
unavailable? Or maybe there is some "padding" configured?

I wonder what does strace say about it.
-- 
Krzysztof Halasa
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