Subject: Re: CCL:Gaussian calculation speed

From: Stuart Purdie <[email-masked]>
Date: Thu, 1 Nov 2001 15:15:05 +0000 (GMT)

On Wed, 31 Oct 2001, Bernd Schubert wrote:

> > Avoid the -X flag to hdparm: I have personally had a case
> > of data loss with such setup.
> 
> But without the -X flag you only enable to use dma-1 --> with a maximum 
> transferrate of 16 MB/s. Using the -X flag you enable Ultra-DMA (ATA-33 -- 
> -X34, ATA-66 -- -X66, etc.).

Some types of disk's, notably those made by Western Digital, and some
controllers, notably the older one made by Via, don't behave quite
correctly with UDMA, and thus if you have a WD disk, or a VIA
motherboard controller, avoid the -X flag.  Otherwise, it aught to be Ok.

---

From: Malcolm Gillies <[email-masked]>
Date: Thu, 01 Nov 2001 18:42:23 +0100

> motherboard controller, avoid the -X flag.  Otherwise, it aught to be Ok.

What documentation I've seen (it's pretty thin) suggests the problem
is confined to the VIA Apollo VP2 chipset. Check your /proc/pci to see
what you have, e.g

 $ less /proc/pci
[...]
  Bus  0, device   1, function  0:
    PCI bridge: VIA Technologies VT 82C598 Apollo MVP3 AGP (rev 0).
      Medium devsel.  Master Capable.  No bursts.  Min Gnt=12.
[...]

Recent VIA chipsets should be fine. My machine uses the VIA Apollo MVP3
chipset (quite common on low-end PIII machines) and I've seen no
problems in six months or so using -X.

I'm running kernel version 2.2.19, and I did need to enable an
'experimental' configuration flag (CONFIG_BLK_DEV_VIA82C586) to make
this work. However, I believe it should work out of the box for the
2.4 series.

Here's a few webpages with some further information:

    http://www.linuxdoc.org/HOWTO/mini/Ultra-DMA.html
    http://lhd.datapower.com/db/dispdriver.php3?DISP?310
    http://www.linux-ide.org/

[unfortunately the information in the Ultra-DMA mini-howto is a couple
 of years old, and partially out of date]

Misbehaving drives should be automatically detected and blacklisted
by the kernel. A (possibly out-of-date) list is included in the
Ultra-DMA mini-HOWTO listed above.

I have also seen patches to the 2.2 and 2.4 series for additional
chipset and feature support (e.g. UDMA100) but I haven't looked into
this. See

    http://www.lwn.net/2000/1102/a/ide.php3

cheers,

Malcolm
--
Malcolm Gillies <[email-masked]>
Post-doctoral researcher
Organic Chemistry, Dept Chemistry,
Technical University of Denmark