Re: [PATCH] speed up SATA

From: Nick Piggin
Date: Sat Mar 27 2004 - 18:40:01 EST

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.
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