On Thu, Jun 20, 2002 at 07:02:28PM +0200, Manuel Bouyer wrote:
> On Thu, Jun 20, 2002 at 02:22:58AM -0400, Charles Shannon Hendrix wrote:
> > [...]
> > Isn't the I/O queue processed in a way that limits heavy I/O processes
> > to give better response time for infrequent I/O processes?  If it is,
> > is this tunable?
> 
> Well, no, it's not unfortunably. It's a simple queue. Disksort will try
> to keep the queue ordered by block numbers (to minimize seeks), which makes
> things even worse: with a large sequential write to a to one partition,
> an I/O for another one will always be put at the end of the queue (or at
> last after the entries of the sequential writes), while newer entries for
> the sequential write will be inserted before this I/O.

That's too bad.  It would be nice if it could break order after a
process had passed some I/O limit.  It limits the effect of a common
tuning method whereby you move applications to separate drives.

Ideally, you would limit the effect to shortening the response time for
the starved and small processes (in terms of I/O), while only slightly
slowing the freight trains that are eating your bandwidth.


-- 
UNIX/Perl/C/Pizza__________________________________shannon@widomaker.com