Date: Mon, 24 Dec 2001 22:59:36 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: "M. Warner Losh" <imp@village.org> Cc: peter.jeremy@alcatel.com.au, phk@critter.freebsd.dk, dg@root.com, bde@zeta.org.au, silby@silby.com, cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/dev/sio sio.c Message-ID: <200112250659.fBP6xaR33808@apollo.backplane.com> References: <20011222193231.D24034@nexus.root.com> <61654.1009097922@critter.freebsd.dk> <20011224162247.B85044@gsmx07.alcatel.com.au> <20011224.234720.15269884.imp@village.org>
next in thread | previous in thread | raw e-mail | index | archive | help
:However, I have had complaints from a few people that have see silo
:overflows on pccard (both with fast interrupts, and slow ones now
:basically forced by 4.4). I don't know if the latencies in normal
:interrupts will all be solved by the HIGH -> MEDH change (since it
:takes us from 2 character times (32us) to 8 character times (128us).
At 115200 baud, 8N1, your character rate is 11.52 KHz which is
86.8 uS / character, so the safety limit is 173 uS vs 694 uS assuming
a standard 16550A with a 16 character FIFO.
:I've seen interrupt latency occasionally be as high as 20-100ms
:(depending on the machine we ran it on) for the parallel port (since
:I'm measuring pps from an atomic clock with it, we can tell these huge
:outliers very easily).
:
:Warner
Latencies that high can probably be traced easily by recording
the interrupted program counter, aka Linux, aka Amiga (Amiga did
it first. Since the Amiga serial port was a piece of crap they
used this trick to track down and fix long interrupt disablements
in the OS core).
-Matt
Matthew Dillon
<dillon@backplane.com>
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe cvs-all" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200112250659.fBP6xaR33808>