lkml.org 
[lkml]   [2004]   [Sep]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] Configure IDE probe delays
Bartlomiej Zolnierkiewicz wrote:
>
>>What determines whether 48 bit addressing will be used then?
>
> Availability of 48-bit addressing feature set and host capabilities
> (some don't support LBA48 when DMA is used etc.).

I haven't examined the "released" IDE drivers in some time,
but one optimisation that can save a LOT of CPU usage
is for the driver to only use LBA48 *when necessary*,
and use LBA28 I/O otherwise.

Each access to an IDE register typically chews up 600+ns,
or the equivalent of a couple thousand instruction executions
on a modern core. Avoiding LBA48 when it's not needed will
save four such accesses per I/O, or about 2.5us.

LBA48 is only needed when (1) the sector count is greater than 256,
and/or (2) the ending sector number >= (1<<28).

I regularly include this optimisation in the drivers I have been
working on since LBA48 first appeared.

Cheers
--
Mark Lord
(hdparm keeper & the original "Linux IDE Guy")
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 14:05    [W:0.100 / U:0.640 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site