Re: [PATCH] Configure IDE probe delays

Lee Revell
2004-09-01T19:08:43Z

On Wed, 2004-09-01 at 11:06, Alan Cox wrote:
> On Mer, 2004-09-01 at 14:20, Mark Lord wrote:
> > LBA48 is only needed when (1) the sector count is greater than 256,
> > and/or (2) the ending sector number >= (1<<28).
>
> I've played with this a bit and in the -ac IDE code it can drop back
> to LBA28 for devices that are small enough not to need LBA48 when the
> controller only supports PIO for LBA48 modes (eg some ALi) as 2.4-ac
> did.
>
> > I regularly include this optimisation in the drivers I have been
> > working on since LBA48 first appeared.
>
> It isn't always a win. You get cut down to 256 sectors per I/O which for
> some workloads has a cost and you need to factor that into the command
> issue choice as well as the last sector number being accessed.
>

I have never been able to measure a decrease in disk throughput in any
disk benchmark with 256 sectors per I/O vs. 1024. This is a modestly
powered desktop with a single drive though. What kinds of workloads
would you expect to be affected by this?

Lee