Re: [gentoo-dev] Disk Performance Issues [AMD Viper plus IDE chipset problems. (wrong udma "autodetection")]

[Dewet Diener]

On Saturday 09 November 2002 20:36, Michael R. Gayeski wrote:
> Are you using 80-wire cables for your drive? The motherboard will
> politely refuse to operate at UDMA 100 without the new cables. Also,

I have no idea about the AMD driver, but my VIA driver creates a 
/proc/ide/via, which contains a lot of useful info on the controller, 
including what type of cables are detected.

> I believe there is a kernel option to force UDMA100 at boot, but I
> seem to remember it not being recommended.

>From Documentation/Configure.help (on 2.4.20-pre10-ac2):

Generic PCI bus-master DMA support
CONFIG_BLK_DEV_IDEDMA_PCI
  If your PCI system uses IDE drive(s) (as opposed to SCSI, say) and
  is capable of bus-master DMA operation (most Pentium PCI systems),
  you will want to say Y here to reduce CPU overhead. You can then use
  the "hdparm" utility to enable DMA for drives for which it was not
  enabled automatically. By default, DMA is not enabled automatically
  for these drives, but you can change that by saying Y to the
  following question "Use DMA by default when available". You can get
[..snip..]
Use PCI DMA by default when available
CONFIG_IDEDMA_PCI_AUTO
  Prior to kernel version 2.1.112, Linux used to automatically use
  DMA for IDE drives and chipsets which support it. Due to concerns
  about a couple of cases where buggy hardware may have caused damage,
  the default is now to NOT use DMA automatically. To revert to the
  previous behaviour, say Y to this question.

  If you suspect your hardware is at all flakey, say N here.
  Do NOT email the IDE kernel people regarding this issue!

  It is normally safe to answer Y to this question unless your
  motherboard uses a VIA VP2 chipset, in which case you should say N.


It shouldn't be a problem at all.

Regards,
Dewet


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