linux-kernel - Re: [PATCH] intel-iommu: Manage iommu

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Message-ID: <1321635658.15493.55.camel@shinybook.infradead.org>
Date:	Fri, 18 Nov 2011 17:00:58 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	rajesh.sankaran@...el.com, iommu@...ts.linux-foundation.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	chrisw@...s-sol.org, ddutile@...hat.com
Subject: Re: [PATCH] intel-iommu: Manage iommu_coherency globally

On Fri, 2011-11-18 at 09:03 -0700, Alex Williamson wrote:
> I can't help but thinking we're just taking the easy, lazy path for VM
> domains when it sounds like we really would prefer to keep the coherency
> set to the least common denominator of the domain rather than the
> platform.  Couldn't we instead force a flush of the domain when we
> transition from coherent to non-coherent?  Not sure I'm qualified to
> write that, but seems like it would keep the efficiency of VM domains
> with no effect to native DMA domains since they'd never trigger such a
> transition.  The below appears as if it would work and probably be OK
> since the unnecessary cache flushes are rare, but they're still
> unnecessary... and the comments/commit log are now wrong.  Thanks,

Yeah, that would make some sense. I was about to knock up some code
which would walk the page tables and use clflush to flush every one...
but wouldn't it be saner just to use wbinvd?

-- 
dwmw2

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