Re: [PATCH] speed up SATA

[Stefan Smietanowski <stesmi@stesmi.com>]

Hi Jeff.

> The "lba48" feature in ATA allows for addressing of sectors > 137GB, and 
> also allows for transfers of up to 64K sector, instead of the 
> traditional 256 sectors in older ATA.
> 
> libata simply limited all transfers to a 200 sectors (just under the 256 
> sector limit).  This was mainly being careful, and making sure I had a 
> solution that worked everywhere.  I also wanted to see how the iommu S/G 
> stuff would shake out.
> 
> Things seem to be looking pretty good, so it's now time to turn on 
> lba48-sized transfers.  Most SATA disks will be lba48 anyway, even the 
> ones smaller than 137GB, for this and other reasons.
> 
> With this simple patch, the max request size goes from 128K to 32MB... 
> so you can imagine this will definitely help performance.  Throughput 
> goes up.  Interrupts go down.  Fun for the whole family.

What will happen when a PATA disk lies behind a Marvel(ous) bridge, as
in most SATA disks today?

Is large transfers mandatory in the LBA48 spec and is LBA48 really
mandatory in SATA?

And yes, I saw that the dmesg showed a Maxtor drive, but I'm uncertain
if that disk of yours has a Marvel chip on or not, since newer Maxtors
might (have) come out (already) without a Marvel chip, I just don't
know.

// Stefan