Date: Fri, 14 Jul 2000 08:46:40 +0200 From: Wilko Bulte <wkb@freebie.demon.nl> To: Stephen McKay <mckay@thehub.com.au> Cc: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net>, "Brandon D. Valentine" <bandix@looksharp.net>, Stefan Esser <se@freebsd.org>, Bill Paul <wpaul@freebsd.org>, freebsd-current@freebsd.org Subject: Re: dc driver and underruns (was: Strangeness with 4.0-S) Message-ID: <20000714084639.B1926@freebie.demon.nl> In-Reply-To: <200007140251.MAA07785@dungeon.home>; from mckay@thehub.com.au on Fri, Jul 14, 2000 at 12:51:14PM %2B1000 References: <200007131622.JAA12738@gndrsh.dnsmgr.net> <200007140251.MAA07785@dungeon.home>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, Jul 14, 2000 at 12:51:14PM +1000, Stephen McKay wrote: > On Thursday, 13th July 2000, "Rodney W. Grimes" wrote: > > >>On Thu, 13 Jul 2000, Stephen McKay wrote: > >> > >>>Does anyone here actually measure these latencies? I know for a fact > >>>that nothing I've ever done would or could be affected by extra latencies > >>>that are as small as the ones we are discussing. Does anybody at all > >>>depend on the start-transmitting-before-DMA-completed feature we are > >>>discussing? > >> > >> I don't like the idea of removing that feature. Perhaps it should be a > >> sysctl or ifconfig option, but it should definitely remain available. > >> Those minute latencies are critical to those of us who use MPI for > >> complex parallel calculations. > > > >I have to agree here. The store and forward adds an approximate > >11uS (by theory under ideal conditions 1500bytes@132MB/s = 11uS, > >practice actually makes this worse as typical PCI does something > >less than 100MB/s or 15uS) to a 120uS packet time on the wire (again, > >ideal, but here given that switches, and infact often cut-through > >switches, are used for these types of things, ideal and practice > >are very close.) > > > >I don't think these folks, nor myself, are wanting^H^H^H^H^H^H^Hilling > >to give up 12.5%. > > OK. It seems that repairing the feature, rather than disabling it is > the most popular option. Still, I am quite interested in finding anyone > who actually measures these things, and is affected by them. These very > same people might be able to trace why we get the underruns in the first > place. I suspect an interaction between the ATA driver and VIA chipsets, > because other than the network, that's all that is operating when I see > the underruns. And my Celeron with a ZX chipset is immune. That theory is not correct, I have seen multiple Alpha machines reporting buffer underruns as well. No ATA disk in sight there.. -- Wilko Bulte http://www.freebsd.org "Do, or do not. There is no try" wilko@freebsd.org http://www.nlfug.nl Yoda - The Empire Strikes Back To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20000714084639.B1926>