linux-kernel - Re: [PATCH 3/3] x86/iommu: use __GFP

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Date:	Mon, 29 Sep 2008 10:56:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
	linux-kernel@...r.kernel.org, fujita.tomonori@....ntt.co.jp
Subject: Re: [PATCH 3/3] x86/iommu: use __GFP_ZERO instead of memset for
	GART


* Joerg Roedel <joerg.roedel@....com> wrote:

> On Sat, Sep 27, 2008 at 08:18:55PM +0200, Ingo Molnar wrote:
> > 
> > another thing:
> > 
> > How hard would it be to add an CONFIG_IOMMU_DEBUG option that forces as 
> > many DMA requests to go via the IOMMU as possible?
> > 
> > This slows things down of course so it's only for debugging - but it 
> > also makes sure that we utilize the IOMMU code to the maximum - which is 
> > not normally the case.
> > 
> > Would be nice to have it .config driven (default-disabled), so that 
> > -tip's randconfig testing can stumble upon it every now and then. I've 
> > got GART test-systems - this way we could find certain types of IOMMU 
> > breakages sooner.
> 
> For AMD IOMMU I disabled the round-robin allocator to stress-test the 
> code. This means that the address allocation bitmap is always 
> traversed from the first bit. In consequence the TLB flushing is 
> stressed a lot (both in hardware and software) because the same DMA 
> addresses are used again and again. For testing I hardcoded it into 
> the driver but I can also make it depend on CONFIG_IOMMU_DEBUG.

yes - could you please make a new option for it, 
CONFIG_IOMMU_DEBUG_FORCE=y or so - and cover all iommus that support it?

	Ingo
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