From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joachim Buermann Subject: Re: overruns with kernel 2.4.19 Date: Wed, 19 Feb 2003 10:35:23 +0100 Sender: linux-serial-owner@vger.kernel.org Message-ID: <20030219103523.5030ed1c.jbuermann@zes.com> References: <11E89240C407D311958800A0C9ACF7D1A33DA0@EXCHANGE> <20030219080309.GA422@lafn.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from inv1253.zes.com (217.5.81.123) by websrvnt02 with MERCUR-SMTP/POP3/IMAP4-Server (v3.10.18 AS-0098309) for ; Wed, 19 Feb 2003 10:40:21 +0100 Received: from inv1253.zes.com (localhost [127.0.0.1]) by inv1253.zes.com (Postfix) with ESMTP id 8A5081F3B1 for ; Wed, 19 Feb 2003 10:35:31 +0100 (CET) Received: from inv1428.zes.com (inv1428.zes.com [192.168.2.28]) by inv1253.zes.com (Postfix) with SMTP id CFAF51F3A8 for ; Wed, 19 Feb 2003 10:35:23 +0100 (CET) In-Reply-To: <20030219080309.GA422@lafn.org> List-Id: linux-serial@vger.kernel.org To: linux serial Hello David, On Wed, 19 Feb 2003 00:03:10 -0800 David Lawyer wrote: > On Tue, Feb 18, 2003 at 04:34:34PM -0800, Ed Vance wrote: > > Hi Joachim and David, > > > > Do I need an external data source to reproduce this, or does it also fail > > with a looped back 115200 baud data stream (ttyS1 -> ttyS0)? I can try it on > > my 333 MHz Pentium II when it frees up in a couple of days. > > > > So, 2.2.20 works okay and 2.4.19 fails. Anybody have a rough idea of when > > the receive data overrun behavior crept in? > > Sorry, but I reached wrong conclusions since I likely tested 2.4.19. > when a backup program was putting a heavy load on the harddisk. > For 2.2.20 there was likely no backup program running. To check out the > situation, I just now tried out surfing the web when a tar program was > running creating a tarball of most of the drive. The number of overruns > was roughly the same for 2.4.19 and 2.2.20: about 1/3 % of the bytes > received. But since the FIFO buffer can hold 16 bytes, its a few > percent of each buffer fetch operation. This seems too high. > > Without tar running, there were few overruns. This indicates that the > problem is due to the interference of the harddisk. It seems just as > bad at the serial port speed of 57.6k as at 115.2k. It still may be > that kernel 2.2.13 is a lot better. This align with my experience on a embedded linux (AMD ELAN 130 MHz). There was a great difference if I using a older harddisk or a newer one. My 2.2.13 desktop machine has also older harddisk and the 2.4.19 machine a modern harddisk, so I will do some tests at home. There are running a 2.2.13 and a 2.4.19 kernel on the same hardware (600 MHz Athlon). Maybe it's not so a kernel problem, as a general behaviour with modern harddisks. But whatever, it doesn't resolve this problem :-( Joachim > > > > > -----Original Message----- From: David Lawyer [mailto:dave@lafn.org] > > Sent: Tuesday, February 18, 2003 3:06 PM To: > > linux-serial@vger.kernel.org Subject: Re: overruns with kernel 2.4.19 > > > > > > On Tue, Feb 18, 2003 at 02:43:46PM +0100, Joachim Buermann wrote: > > > Hello all, > > > > > > I`m using linux mandrake kernel 2.4.19 on a 2 GHz Pentium 4 with 128 > > > MByte RAM. The serial port /dev/cua0 is connected to a external > > > device and receives data with 115200 Baud. > > The cua devices have been obsolete for some time. > > > > > > Unfortunately I get a lot of fifo overruns. I have unmasked the hda > > > interrupts with: > > > > > > hdparm -u1 /dev/hda > > > > > > also set the low_latency flag in the serial driver. The harddisk dma > > > couldn't disabled. > > > > > > I'm wonder at this behavior, because with a lower machine (Pentium I > > > 120 MHz, Kernel 2.2.13) I get overruns only once in a blue moon. And > > > I expected, that a 2 GHz machine should be quick enough, to responds > > > to the serial interrupts. > > > > Almost the same for me. On a Pentium I 90 MHz I get no overruns with > > kernel 2.2.20, but get hundreds of overruns on the same machine with > > kernel 2.4.19. Something is wrong with the software. > > > > David Lawyer > - > To unsubscribe from this list: send the line "unsubscribe linux-serial" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html