Path: utzoo!attcan!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucdavis!iris!auyeung
From: auyeung@iris.ucdavis.edu (Tak (UlTech) AuYeung)
Newsgroups: comp.sys.amiga.tech
Subject: Smooth Operator (for disks)
Keywords: disk schedule multi-process optimizer smooth seek
Message-ID: <5850@ucdavis.ucdavis.edu>
Date: 7 Nov 89 17:37:35 GMT
Sender: uucp@ucdavis.ucdavis.edu
Reply-To: auyeung@iris.ucdavis.edu (Tak (UlTech) AuYeung)
Organization: U.C. Davis - Department of Electrical Engineering and Computer Science
Lines: 36

Greetings to all the pros in AmigaLand!  I'm not even close to
a pro in ALand, and this is why I have to ask for YOUR help!

I noticed that disk accesses are mostly delayed by the seek time
of the disk head (vs. the actual transfer time), especially in
a multitasking environment.  Even if you use a disk optimizer,
two processes trying to access data on different cylinders will
make the disk seeking mechanism very busy.  For hard disks
owner, this problem may be minute, but for most floppy-only
Amigans, the seek operation is noisy, slow and bad for the
media (floppy disks).

So are there any alternative disk drivers that optimizes seek
operations so that the disk head scans through the cylinders
in a smoother manner?  For example, we can keep a SeekQ sorted
by the cylinder number and the driver always pick the next
SeekRequest that is closest to the current one first in
decreasing order until it hits the tail of Q, and then in
increasing order until it hits the head of Q.  This eliminates
starvation for the de/increasing order is monotonic.  Of
course, there are more elegant scheduling algorithms, but this
simple one is all I can think of now.  E.g., we may serve all
the requests in the neighborhood first, then go on to the
next district...

If there is no existing s/w to do this, could any one of you
pros write a PD smooth disk driver?  I think a lot of amigans
will appreciate your kind contribution!

Thanks for your attention!

--Tak
      #   #    =====         everything's only what it seems to be
      #   # #    # ===\ /=== #   # >>>>> auyeung@iris.ucdavis.edu
      #   # #    # ----X     #---# >>>>> Tak-Ying (UlTech) AuYeung
      \===/ \=== # ===/ \=== #   # >>>>> Logical Entity in Netland