Re: sg regression in 2.6.16-rc5

[Jeff Garzik]

Linus Torvalds wrote:
> For example, I think the IDE driver defaults to a maximum transfer of 256 
> sectors, and the same number of max scatter-gather entries. Some 
> controllers will actually lower that, due to silly hw problems.

Yep.  Just to be specific:

256 max sectors IDE driver, 200 max sectors libata (due to driver not 
hardware).

256 max s/g entries hardware limit, but due to a IOMMU merging worst 
case libata (IDE driver too?) winds up with a 128 entry practical limit.

Newer SATA controllers eliminate the s/g entry limit and DMA boundary 
limits, but its still 256 max-sectors for ATAPI (64k for LBA48 ATA).

	Jeff


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