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    SubjectRe: [Fdutils] DMA cache consistency bug introduced in 2.6.28
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    On Tue, 2010-01-12 at 01:04 -0800, Mark Hounschell wrote:
    > On 01/11/2010 07:19 PM, Pallipadi, Venkatesh wrote:
    > >
    > > Sorry for not following up on this. We have narrowed this down to HPET
    > > MSI and floppy DMA. I still don't know how HPET MSI interrupts are
    > > breaking floppy DMA.
    > >
    > > You are seeing the problem on two different systems. Correct? Do you
    > > have any system where this works with HPET MSI enabled?
    > >
    >
    > I see the problem on every system in which the HPET2 shows up in
    > /proc/interrupts. The machines that work with HPET enabled don't show HPET
    > at all in /proc/interrupts. I have some of each. All the boxes that fail
    > here use the (AMD) 790x series chip sets.
    >
    > > Couple of options on how we can go about this one:
    > > 1) Change the HPET-MSI change to not get activated when there are no
    > > C-states with LAPIC stoppage involved. This will resolve the problem on
    > > the systems you reported as there are no deep C-states. But, I fear that
    > > with the actual problem unresolved, we may hit it in future with this or
    > > some other platform having same issue with CPUs that support deep
    > > C-state.
    > > 2) Try this testcase on few other platforms that support HPET-MSI and
    > > deep C-states and check how widespread the problem is and then add a
    > > whitelist-blacklist for HPET MSI usage.
    > >
    > > I think, for 2.6.33 option 1 is better. Will work on that and send in
    > > patches for you test.
    > >
    >

    Mark,

    I just sent out a patchset that should workaround the problem here. Can
    you check and let me know whether thats the case.

    We will still need a simpler/smaller workaround for .33. Will send a
    patch for that soon.

    Also, are you testing this with usb floppy controller? I tried to test
    it on my end, but fdformat doesn't seem to like my usb floppy drive. I
    tried, 'ufiformat -f 1440 <dev>', with which I am not able to reproduce
    the failure on any of my boxes. Not sure whether that really means I
    don't hit this bug or that is going through totally different code path.

    Thanks,
    Venki




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