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SubjectRe: PIO disk writes using 100% system time and performing poorly with VIA vt82c686b on kernels 2.2 & 2.4
On Tue, Apr 24, 2001 at 07:19:41PM -0400, Ignacio Monge wrote:

> I have VIA686a too and a UDMA100 hard disk.
> This is my cat /proc/ide/via:
> ----------VIA BusMastering IDE Configuration----------------
> Driver Version: 3.23
> South Bridge: VIA vt82c686a
> Revision: ISA 0x22 IDE 0x10
> Highest DMA rate: UDMA66
> BM-DMA base: 0xb800
> PCI clock: 33MHz
> -----------------------Primary IDE-------Secondary IDE------
> Enabled: yes yes
> Cable Type: 40w 40w
> -------------------drive0----drive1----drive2----drive3-----
> Transfer Mode: DMA UDMA PIO PIO
> Address Setup: 30ns 30ns 120ns 120ns
> Cmd Active: 90ns 90ns 480ns 480ns
> Cmd Recovery: 30ns 30ns 480ns 480ns
> Data Active: 90ns 90ns 330ns 330ns
> Data Recovery: 30ns 30ns 270ns 270ns
> Cycle Time: 120ns 60ns 600ns 600ns
> Transfer Rate: 16.5MB/s 33.0MB/s 3.3MB/s 3.3MB/s
> As you can see, l use UDMA66 instead UDMA100.

You use UDMA33 dor your second drive and MWDMA16 for your first.
Check your BIOS UDMA enable settings.

> I don't know why. Maybe VIA vt82c686a doesn't support it?

Yes, it supports modes only up to 66 MB/sec.

> I have answering in this list a days ago about this problem. but none seems to have a question. Like you, my system goes down when I try to compile something (I have a 394 Mb of RAM and a 1 Ghz processor).
> Although, my hdparm output is this:
> /dev/hde2:
> Timing buffer-cache reads: 128 MB in 0.79 seconds =162.03 MB/sec
> Timing buffered disk reads: 64 MB in 2.44 seconds = 26.23 MB/sec
> and sometime looks better.

26 megabytes per second is quite surprising in your setup

> I don't know is this is a problem with the VIA kernel driver or not. But the system doesn't seem to work fine since 2.4.2 or 2.4.1 kernel. I hope (plz!) this problem will be fixed in future.

You can disable the VIA driver.

> PS: in cat /proc/ide/via I see "Cable Type: 40w 40w"... Is it right? I have a 80w cable, not 40.

Check your BIOS settings, if you have disabled UDMA in the BIOS, the
driver can't detect the cable. If that doesn't work, use "ide0=ata66"
on the kernel command line.

Vojtech Pavlik
SuSE Labs
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