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algorithmperlschedulingtimingdisk

Hard Disk scheduling simulator algorithm (track to track timing) Perl

I am trying to get to grips with perl. I am trying to write a few scripts as a scheduling simulator. FCFS, SSTF and Scan and Look

I have one array with a list of block requests and another to act as the buffer. First I will copy over the first request, then I need to work out the time it takes to get from the first to the second block.

the buffer reads in blocks at 1 per ms, seek, search and access time are all 1ms to make the calculations a bit easier, the simulator always starts on block 1 track 1.

http://postimg.org/image/d9osb8tkj/

so if the first block is 5, the search time will be 3ms to traverse to the start of the 5th block, the seek time will be zero as its on the same track and the access time to read the block will always be 1ms. This means that the time for this request will be 4ms so the simulator will read in the next 4 requests into the buffer. In first come first served this will just be the order that the requests are served.

So if the next request to serve is 12 the arm is on the end of the 5th block so will take 2ms to get to the right track then 1ms to get to the start of the 12th block and another 1ms to access it.

I was just wondering if anyone could give me some idea how I could express this as an algorithm. Just some pointers would be much appreciated.

Solution

  • write a class HardDiskSim::Abstract, 3 subs seek_time(), spin_time(), and read_time()

    Write a subclass of AbstractDisk for each different set of values/logic for the three methods.

    Fir example:

     package HardDiskSim::Simple;
 use base qw(HardDiskSim::Abstract);

 our $SECTORS_PER_TRACK = 5;
 our $SEEK_TTIM_PER_TRACK = 1;
 sub read_time { return 1 }
 sub seek_time { 
   my $block = @_;
   my $tracks_to_seek = int($block / $SECTORS_PER_TRACK);
   return $tracks_to_seek * $SEEK_TTIM_PER_TRACK;
 }

 sub spin_time {
    # compute head position at end of seek using seek time and RPM of disk
    # compute number of sectors to spin past using computed head position
    # return number_of_sectors_to_spin_past * time_per_sector
 }

    I had the fun of writing this kind of code in Fortran, for a class, back in 1985.