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SubjectRe: Disk Performance
On Sun, 11 Nov 2001, Maxwell Spangler wrote:

> On Sun, 11 Nov 2001, Andre Hedrick wrote:
> > The significance of the tuning code is not just for init events.
> > Linux is the first and only OS to have the autodma down grade feature
> > (Intel borrowed my model, approved by me). This allows for kernel to auto
> > reconfigure the drive to stablize the transfer rates to protect the data.
> > Of course the ATA hardware has iCRC's un Ultra modes, but excessive
> > retries which are/will be successfully defeat the power of Ultra
> > transfers. Therefore the tuning code in conjunction the the
> > auto-down-grade functions will reduce the transfer rates until the iCRC's
> > go away. This is the 0x84/0x51 error pairs. There are various reasons
> > that can cause this error to occur; however, the first stage is to
> > stablize the transport data path and then allow the SA or EU to examine
> > the problems.
> So the system will boot at ATA100, for example, and if errors are seen,
> downgrade step by step until a satisfactory level is reached. Perhaps, ATA66
> or ATA33 and the system would continue proper operation still at a "somewhat
> fast" (as compared to PIO) speed level AND in DMA mode, not PIO. My situation
> with the 6.31 driver has DMA being disabled by the driver when errors are
> seen, as I think you have clearly stated.
> ?? I'm assuming no to this, but I'm curious: Is there any chance the driver
> would "speed up" the transfers? Ie: after a period of time at ATA33, would it
> try ATA66, 100 again? I suppose this makes more sense for things like
> serial/modem communications where problems could come and go, but if one is
> experiencing problems between the ATA circuitry, cable and drive, they'll
> start good, get worse and never recover..?
> -------------------------------------------------------------------------------
> Maxwell Spangler
> Program Writer
> Greenbelt, Maryland, U.S.A.
> Washington D.C. Metropolitan Area

Hi Maxwell,

A system will launch PIO and if there is a driver it will be feature
enabled to max performance and auto scaled if there are problems

The current code has a mistake that is not fatal, but regardless wrong.

Ultra 100|66|44|33|25|16 -- MW DMA 2|1|0 -- SW DMA 2|1|0 -- PIO4
5 4 3 2 1 0

The fault is that you lose the iCRC features in Ultra so dropping to
Multi/Single word DMAs only gain speed w/ out a safety net.

The current patch code series does a single reduction of transfer rate per
counting 10 iCRC events, and no other errors are allowed.

Ultra 133|100|66|44|33|25|16|---PIO4
6 5 4 3 2 1 0 ---

You need to enable the chipset code otherwise the driver will not allow
DMA to run in a sane mode.


Andre Hedrick
CEO/President, LAD Storage Consulting Group
Linux ATA Development
Linux Disk Certification Project

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