Date: Sun, 05 Dec 1999 20:41:31 -0800 From: Mike Smith <msmith@freebsd.org> To: mjacob@feral.com Cc: hackers@FreeBSD.ORG Subject: Re: tty level buffer overflows Message-ID: <199912060441.UAA00805@mass.cdrom.com> In-Reply-To: Your message of "Sat, 04 Dec 1999 09:36:30 PST." <Pine.BSF.4.10.9912040854180.27711-100000@beppo.feral.com>
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> > > Er, you should read the sio(4) manpage too. tty-level buffer overflows > > have nothing to do with interrupt latency/execution time. > > You mean this: > > sio%d: tty-level buffer overflow. Problem in the application. Input has > arrived faster than the given module could process it and some has been > lost. Yup. Ignore the "problem in the application" part, as that predicates that the kernel and driver are working properly, which doesn't seem to be the case. The problem here is that the buffer between the top side of the driver and the application isn't being drained fast enough. It would be educational to know what the app is sleeping on when these messages are emitted; just dropping to ddb and using 'ps' would probably be enough. There has to be some reason that the process is either not being woken when data arrives, or is being held up somewhere else for long enough that the clist overflows. Does the problem still manifest with the recent scheduler changes? Perhaps the comms processes are being unfairly scheduled against for some reason? > Normally I might agree with this, but I use a tty line on a 150Mhz i386 to > be a serial console for another freebsd box. This is a NS16550A with a 16 > byte fifo. This systems is effectively idle except for this task. So, I'm > running tip and I get constant tty-level buffer overflows at 9600 baud. > > I also have a 8 (well, 6 now since I moved and one of the system boards > blew a backplane interface chip) 50 Mhz processor SS1000 running Solaris > 2.6. It has 5 Zilog (2 byte fifo) 8530 chips running constant console > sessions with regular large amounts of output (debugging and panicing > other solaris systems for Fibre Channel work) via tip. There has never > been a lost character that I can see except due to power outage. I am > convinced to a moral certainty and beyond a reasonable doubt that if I had > a single 50Mhz processor I'd have the same experience. > > Since the Solaris tip and the FreeBSD tip are essentially identical (both > derive from BSD 4.X tip), I'd like to try and understand how this is an > application problem :-). > > -matt > > > > -- \\ Give a man a fish, and you feed him for a day. \\ Mike Smith \\ Tell him he should learn how to fish himself, \\ msmith@freebsd.org \\ and he'll hate you for a lifetime. \\ msmith@cdrom.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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