[lkml]   [1998]   [Nov]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: elevator algorithm bug in ll_rw_blk.c
On Sun, 15 Nov 1998, Riley Williams wrote:

> That overlooks the fact that for a unidirectional scan, the head still
> has to be scanned back across the whole width of the disk, so you're
> actually saying that one is better off making all suchlike seeks taake
> 1+1=2 rather than letting some of them take 1/2+1/2=1 - and I have to
> say that I disagree with you...

You are missing the point. A return scan takes a short time, the time
taken is in stopping the heads to service a request. The extra cost of the
return is usually accepted as a tradeoff for the fairness.

Most os textbooks have a chapter on filesystem design that treats this
topic. They usually explain why a one-way scan is usually used.

Peter Svensson ! Pgp key available by finger, fingerprint:
<> ! 8A E9 20 98 C1 FF 43 E3 07 FD B9 0A 80 72 70 AF
<> !
Remember, Luke, your source will be with you... always...

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
Please read the FAQ at

 \ /
  Last update: 2005-03-22 13:45    [W:0.146 / U:0.204 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site