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SubjectRe: PIO disk writes using 100% system time and performing poorly with VIA vt82c686b on kernels 2.2 & 2.4

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
Master Read Cycle IRDY: 0ws
Master Write Cycle IRDY: 0ws
BM IDE Status Register Read Retry: yes
Max DRDY Pulse Width: No limit
-----------------------Primary IDE-------Secondary IDE------
Read DMA FIFO flush: yes yes
End Sector FIFO flush: no no
Prefetch Buffer: no no
Post Write Buffer: no no
Enabled: yes yes
Simplex only: no no
Cable Type: 40w 40w
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. I don't know why. Maybe VIA vt82c686a doesn't support it? 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:
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.

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.

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

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