kern/51982: sio1: interrupt-level buffer overflows

[Ian Freislich]

The following reply was made to PR kern/51982; it has been noted by GNATS.

From: "Ian Freislich" <ianf at za.uu.net>
To: Bruce Evans <bde at zeta.org.au>
Cc: FreeBSD-gnats-submit at freebsd.org, freebsd-bugs at freebsd.org
Subject: Re: kern/51982: sio1: interrupt-level buffer overflows 
Date: Fri, 09 May 2003 09:29:53 +0200

 Bruce Evans wrote:
 > On Mon, 5 May 2003, Ian Freislich wrote:
 > 
 > > >Description:
 > > 	Transferring data at "high" speed 115200bps over the serial
 > > 	line (even though the actual incoming line stream is about
 > > 	37000bps according to the modem LCD panel) results in the
 > > 	following messages on the console at a rate of about 1 log
 > > 	line every 10 to 15 seconds.
 > >
 > > 	These buffer overruns have gradually become more frequent
 > > 	from about 3 lines and 24 overruns a day around September
 > > 	2002 (when I started running Current - 4.x does not suffer
 > > 	from this) to the current flurry.
 > 
 > -current has excessive interrupt latency caused by Giant locking almost
 > everything.
 > 
 > Try changing this line in sio.c:
 > 
 > 	cp4ticks = speed / 10 / hz * 4;
 > 
 > to something like:
 > 
 > 	cp4ticks = speed / 10 / hz * 40;
 
 Thanks.  Making this change seems to have fixed the problem.  Will
 this be committed or do I need to maintain this privately until the
 larger interrupt latency problem is fixed?
 
 > Transient interrupt latency problems are supposed to be made harmless
 > by using rts flow control.  There is a PR (maybe from you?) about rts
 > flow control apparently not working for one modem.
 
 Not me.
 
 Ian