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

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Date:	Thu, 14 Jan 2010 18:01:57 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	"dmarkh@....rr.com" <dmarkh@....rr.com>
Cc:	"markh@...pro.net" <markh@...pro.net>,
	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alain Knaff <alain@...ff.lu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"fdutils@...tils.linux.lu" <fdutils@...tils.linux.lu>,
	"Li, Shaohua" <shaohua.li@...el.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [Fdutils] DMA cache consistency bug introduced in 2.6.28

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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