lkml.org 
[lkml]   [2003]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: 2.5.59-mm5
From
Date
On Fri, 24 Jan 2003 21:04:34 +0100, Jens Axboe said:

> Nicks comment refers to the block layer situation, we obviously cannot
> merge reads and writes there. You would basically have to rewrite the
> entire request submission structure and break all drivers. And for zero
> benefit. Face it, it would be stupid to even attempt such a manuever.

As I *said* - "hairy beyond benefit", not "cant".

> Since you bring it up, you must know if a device which can take a single
> command that says "read blocks a to b, and write blocks x to z"? Even
> such thing existed,

They do exist.

IBM mainframe disks (the 3330/50/80 series) are able to do much more than that
in one CCW chain So it was *quite* possible to even express things like "Go to
this cylinder/track, search for each record that has value XYZ in the 'key'
field, and if found, write value ABC in the data field". (In fact, the DASD I/O
opcodes for CCW chains are Turing-complete).

> it would be much better implemented by the driver
> as pulling more requests of the queue and constructing these weirdo

The only operating system I'm aware of that actually uses that stuff is MVS.

> So I quite agree with the "obviously".

My complaint was the confusion of "obviously cant" with "we have decided we
don't want to".

/Valdis
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2005-03-22 13:32    [W:1.206 / U:0.916 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site