Date: Sun, 23 Dec 2001 14:41:16 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: David Greenman <dg@root.com> Cc: Mike Silbersack <silby@silby.com>, Matt Dillon <dillon@FreeBSD.org>, <cvs-committers@FreeBSD.org>, <cvs-all@FreeBSD.org> Subject: Re: cvs commit: src/sys/dev/sio sio.c Message-ID: <20011223143011.G10441-100000@gamplex.bde.org> In-Reply-To: <20011222191321.B24034@nexus.root.com>
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On Sat, 22 Dec 2001, David Greenman wrote: > >The driver used to have dynamic fifo trigger reduction, mainly to > >support many active sio devices, but this was found harmful and backed > >out: > > > >! RCS file: /home/ncvs/src/sys/dev/sio/sio.c,v > >! Working file: sio.c > >! head: 1.353 > >! ... > >! ---------------------------- > >! revision 1.53 > >! date: 1994/09/21 19:39:25; author: davidg; state: Exp; lines: +3 -1 > >! #if 0'd evil dynamic fifo trigger level adjustment; it just bit me and > >! a couple of other people again. > >! ---------------------------- > > You know, it's really weird to see stuff that I wrote from more than > 7 years ago. I can only imagine how Kirk feels when he sees log messages > from the 80's. :-) At least if they have been untouched for that long then they were probably correct :-). > As I recall, the dynamic adjustment increased interrupt overhead each > time it ratcheted down, causing it to be even more likely to lower it > further until it was "1", disabling the overhead reduction benefits of > the fifo completely. The cure became worse than the disease. I once planned to bring this back, at least as an option, with the ratcheting down limited to 1 step. I never got around to this because the problem seemed to have gone away except for unusual hardware combinations. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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