Re: [Fdutils] DMA cache consistency bug introduced in 2.6.28

From: Mark Hounschell
Date: Fri Jan 15 2010 - 13:03:05 EST

On 01/14/2010 09:01 PM, Pallipadi, Venkatesh wrote:
> 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.

Yes, it does seem to fix the issue. The floppy formats and /proc/interrupts
look normal with nothing going on with the hpet2 msi.


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