Date: Sat, 22 Dec 2001 19:34:45 -0800 From: David Greenman <dg@root.com> To: Bruce Evans <bde@zeta.org.au> 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: <20011222193445.E24034@nexus.root.com> In-Reply-To: <20011223143011.G10441-100000@gamplex.bde.org>; from bde@zeta.org.au on Sun, Dec 23, 2001 at 02:41:16PM %2B1100 References: <20011222191321.B24034@nexus.root.com> <20011223143011.G10441-100000@gamplex.bde.org>
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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 :-). Correct for the time, perhaps, but hardware has gotten faster and FreeBSD kernel latency has apparantly gotten worse. >> 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. Perhaps reduce it to the mid-point (8), but not below that. -DG David Greenman Co-founder, The FreeBSD Project - http://www.freebsd.org President, TeraSolutions, Inc. - http://www.terasolutions.com Pave the road of life with opportunities. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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