Re: [PATCH] take 48-bit lba a bit further

[Jens Axboe <axboe@suse.de>]

On Sun, Apr 06 2003, John Bradford wrote:
> > Thanks for taking the previous bit Alan, here's an incremental update to
> > 2.5.66-ac2. Just cleans up the 'when to use 48-bit lba' logic a bit per
> > Andries suggestion, and also expands the request size for 48-bit lba
> > capable drives to 512KiB.
> > 
> > Works perfectly in testing here, ext2/3 generates nice big 512KiB
> > requests and the drive flies.
> 
> Then, don't we want to be using 48-bit lba all the time on compatible devices
> instead of falling back to 28-bit when possible to save a small amount of
> instruction overhead?  (Or is that what we're doing already?  I haven't really
> had the time to follow this thread).

The logic in the patch is to enable large requests _if_ the drive can do
48-bit lba. However, we will only use 48-bit lba commands if the request
is either beyond 2^28 sectors _or_ bigger than 256 sectors since neither
of these can be addressed with 28-bit lba.

See rq_lba48 in the patch, it explains it.

-- 
Jens Axboe