Message-ID: <44089C34.2030604@garzik.org>
Date: Fri, 03 Mar 2006 14:42:44 -0500
From: Jeff Garzik <jeff@garzik.org>
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To: Linus Torvalds <torvalds@osdl.org>
CC: Steve Byan <smb@egenera.com>, Mark Lord <lkml@rtr.ca>,
       Matthias Andree <matthias.andree@gmx.de>,
       Douglas Gilbert <dougg@torque.net>, Mark Rustad <mrustad@mac.com>,
       linux-scsi@vger.kernel.org,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: sg regression in 2.6.16-rc5
References: <E94491DE-8378-41DC-9C01-E8C1C91B6B4E@mac.com> <4404AA2A.5010703@torque.net> <20060301083824.GA9871@merlin.emma.line.org> <Pine.LNX.4.64.0603011027400.22647@g5.osdl.org> <4405E8AA.1090803@rtr.ca> <Pine.LNX.4.64.0603011036110.22647@g5.osdl.org> <CF493E39-B369-46D8-85EE-013F2484F1C6@egenera.com> <Pine.LNX.4.64.0603031035140.22647@g5.osdl.org>
In-Reply-To: <Pine.LNX.4.64.0603031035140.22647@g5.osdl.org>
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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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