From: Chris Wright <chrisw@sous-sol.org>
To: Roland Dreier <roland@purestorage.com>
Cc: David Woodhouse <dwmw2@infradead.org>,
Alex Williamson <alex.williamson@redhat.com>,
iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org, chrisw@sous-sol.org,
ddutile@redhat.com
Subject: Re: [PATCH] intel-iommu: Default to non-coherent for domains unattached to iommus
Date: Fri, 11 Nov 2011 16:51:00 -0800 [thread overview]
Message-ID: <20111112005100.GR14486@sequoia.sous-sol.org> (raw)
In-Reply-To: <CAL1RGDXZjKhA++3eFVPbazixaM7Q_JfBJyLKE0xjBs+sK55idg@mail.gmail.com>
* Roland Dreier (roland@purestorage.com) wrote:
> On Fri, Nov 11, 2011 at 4:37 PM, David Woodhouse <dwmw2@infradead.org> wrote:
> > This brain-damage only affects the first chipsets
> > from before we worked out that cache incoherency was a *really* f*cking
> > stupid idea, doesn't it?
>
> As we talked about at KS, I have some Westmere EP (ie latest
> and greatest server platform) systems where the BIOS exposes
> an option that allows choosing VT-d coherency on or off, and
> defaults it to "off".
That's just more brain damage AFAICT. Esp. if you do performance
testing (and choose not to use passthrough mode)... have and it's
quite measurable. I switched default to on long time ago, w/out
issue.
> What is the "official" Intel line on coherency with Westmere and
> Tylersburg -- because as I also mentioned, I was seeing some
> problems with VT-d and the default "coherency off" setting that
> looked like the IOMMU HW is getting stale PTEs (ie a missing
> or not working cache flush).
That sounds like sw bugs more than official recommendation issue.
thanks,
-chris
next prev parent reply other threads:[~2011-11-12 0:51 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-11 22:49 [PATCH] intel-iommu: Default to non-coherent for domains unattached to iommus Alex Williamson
2011-11-12 0:17 ` Chris Wright
2011-11-12 0:37 ` David Woodhouse
2011-11-12 0:45 ` Chris Wright
2011-11-12 0:47 ` Chris Wright
2011-11-12 0:51 ` David Woodhouse
2011-11-12 0:58 ` Chris Wright
2011-11-12 1:03 ` David Woodhouse
2011-11-12 0:46 ` Roland Dreier
2011-11-12 0:51 ` Chris Wright [this message]
2011-11-12 0:55 ` David Woodhouse
2011-11-12 1:08 ` Chris Wright
2011-11-12 1:20 ` David Woodhouse
2011-11-15 7:12 ` cody
2011-11-15 4:54 ` Chris Wright
2011-11-15 5:55 ` Kai Huang
2011-11-12 1:30 ` Roland Dreier
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