# idebus= parameter

## edub

Hi folks,

Have done some searches on this parameter and also some kernel doc reading, and still looking for an answer to my question....which is:  I think my bus speed is 133...the highest speed I can specify using this parameter is 66?  (i.e., idebus=66).

Am I misunderstanding how this parameter works?  Pointers to docs about this would be appreciated along with thoughts on the matter.

Thanks alot,

E

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## Moon

If i'm not mistaken the message at boot time

says it assumes IDEBUS=xxx for PIO-Modes,

since you're most likely running with DMA enabled this setting should have no effect.

Moon

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## Moon

If i'm not mistaken the message at boot time

says it assumes IDEBUS=xxx for PIO-Modes,

since you're most likely running with DMA enabled this setting should have no effect.

Moon

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## edub

DMA gets disabled during boot for whatever reason, so I turn it on via a local.start (i think that's the filename) instruction, which results in successfully turning it on for my drive.  However, if I do not specify idebus=66 (the highest setting available for the idebus= parameter), I agree that dmsg says "assuming idebus=33".  Setting the idebus=66 param at boot time improves this to an idebus speed of 66, which is good, but not as good as 133.  Am I missing something that DMA does to improve this itself?  Perhaps turning on DMA improves the bus speed over and above the 66 set by the kernel at boot?

Thanks for the help!

E

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## rommel

what chipset do you have on your mainboard, and did you enable any support for it in the kernel?

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## Hypnos

Try benchmarking both options using "hdparm -Tt".  I have found that the idebus parameters has zero effect once the kernel is using DMA with the disk.

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## edub

Thanks for the thoughts, rommel & Hypnos.  I will do some further reseach and post here with anything notable.  Thanks again.

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