Date: Thu, 31 Aug 1995 17:51:02 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: gibbs@freefall.FreeBSD.org (Justin T. Gibbs) Cc: FreeBSD-hackers@freebsd.org Subject: Re: 4GB Drives Message-ID: <199509010051.RAA13303@gndrsh.aac.dev.com> In-Reply-To: <199509010034.RAA03131@freefall.FreeBSD.org> from "Justin T. Gibbs" at Aug 31, 95 05:34:16 pm
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> > >> One thing to watch out for is that even without tagged queuing, you > >> can get up to two requests per target sitting on the board. You'll > > > >Those are the 2 I need to eliminate for my analysis. Any quick dirty > >hack I can do to turn them off? > > Then set the number of commands that the scsi system is allowed to queue > to 1 instead of 2. Look on line 882 of aic7xxx.c: > > ahc->sc_link.opennings = 2; > > Should be changed to 1. THANKS!! Finding that stuff buried in all the scsi code is painful. > >> have to blink something when the command that gets taken off the queue > >> is for a target that has an active command pending since it will re-queue > >> the transaction in that case. This will happen when the first transaction > >> to the disk disconnects to do the seek. > > > >Test case has already eliminated all seeks. Seeks do not occur as my total > >transfer is smaller than 1 cylinder * stripe width. I am trying to find > >the proper parameters and emperical data to improve my theoritcal caclulations > >and formulas. I can't find the errors in these algorithms without some > >correlation to real measured data to find the bad assumptions in them :-(. > > Hmm. Are you sure that the drive will not disconnect even for a short time > after receiving its command? Darn sure, I effectivly disabled disconnect/reconnect by tweaking the buffer full/empty ratios and a few other parameters in mode page 2. > >The data I need is being very difficult to obtain without spending major > >dollars on a scsi bus analyzer and a large logic analyzer :-(. I guess > >I could go out to the labs some weekend, but it is a pain to check in this > >much equipment. > > I would think that a scope attached to the led line would be sufficient > for most of the timing. Yes, it should be, but if I have things like command queueing occuring I can not correlate the edge created in the stripe layer with the edge created by the LED, it may be skewed by 1 cycle. Or I could go get a $10k storage scope and use single events :-). -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Reliable computers for FreeBSD
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