Re: [PATCH] speed up SATA

[Nick Piggin <nickpiggin@yahoo.com.au>]

Jeff Garzik wrote:
> 
> 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.
> 

Hi Jeff,
I think 32MB is too much. You incur latency and lose
scheduling grainularity. I bet returns start diminishing
pretty quickly after 1MB or so.