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List:       kvm
Subject:    Re: IOMMU groups: better with Intel root ports, or with PEX8606 switch?
From:       Alex Williamson <alex.williamson () redhat ! com>
Date:       2013-12-30 4:16:45
Message-ID: 1388377005.4981.69.camel () ul30vt ! home
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On Sat, 2013-12-28 at 23:32 -0800, Dana Goyette wrote:
> On 12/28/2013 7:23 PM, Alex Williamson wrote:
> > On Sat, 2013-12-28 at 18:31 -0800, Dana Goyette wrote:
> >> I have purchased both a SuperMicro X10SAE and an X10SAT, and I need to
> >> soon decide which one to keep.
> >>
> >> The SuperMicro X10SAT has all the PCIe x1 slots hidden behind a PLX
> >> PEX8066 switch, which claims to support ACS.  I'd expect the devices
> >> downstream of the PLX switch to be in separate groups.
> >>
> >> With Linux 3.13-rc5 and "enable overrides for missing ACS capabilities"
> >> applied and set for the Intel root ports, the devices behind the switch
> >> remain stuck in the same group.
> >>
> >> In terms of passing devices to different VMs, which is better: all
> >> devices on different root ports, or all devices behind the one
> >> ACS-supporting switch?
> >
> > Can you provide lspci -vvv info?  If you're getting that for groups
> > either the switch has ACS capabilities, but doesn't support the features
> > we need or we're doing something wrong.  Thanks,
> >
> I initially tried attaching the output as a .txt file, but it's too 
> large.  Anyway, here's the output of lspci -nnvvv (you may notice that I 
> moved the Radeon to a different slot).

Well, something seems amiss since the downstream switch ports all seem
to support and enable the correct set of ACS capabilities.  I'm tending
to suspect something wrong with the ACS override patch or how it's being
used since your IOMMU group is still based at the root port.  Each root
port is isolated from the other root ports though, so something is
happening with the override patch.  Can you provide the kernel command
line you use to enable ACS overrides and the override patch you're
using, as it applies to 3.13-rc5?  Thanks,

Alex

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