linux-kernel - Re: [PATCH] intel-iommu: Default to non-coherent for domains unattached to iommus

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Message-ID: <20111115045404.GC30247@sequoia.sous-sol.org>
Date:	Mon, 14 Nov 2011 20:54:04 -0800
From:	Chris Wright <chrisw@...s-sol.org>
To:	cody <mail.kai.huang@...il.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Roland Dreier <roland@...estorage.com>,
	linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH] intel-iommu: Default to non-coherent for domains
 unattached to iommus

* cody (mail.kai.huang@...il.com) wrote:
> On 11/11/2011 05:20 PM, David Woodhouse wrote:
> >On Fri, 2011-11-11 at 17:08 -0800, Chris Wright wrote:
> >>On a slightly separate, but performance related note...have you ever
> >>tried using the hw queue?  Currently we only have a sw queue, but the
> >>submission path for invalidations doesn't really queue (unless I missed
> >>it).  It seems to pull from the software queue and submit/wait,
> >>submit/wait...Seems simple enough to submit the whole queue and then
> >>issue the wait.
> >I have a feeling we trigger errata if we do that — although if we're
> >only doing it for an emulated IOMMU that shouldn't be an issue.
> >
> What does the emulated IOMMU here? Does it mean the emulated IOMMU
> exposed to guest VM?

Yes.  So for KVM, the IOMMU emulation would be in QEMU.

thanks,
-chris
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