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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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