[Bug 201753] AMD-Vi: Unable to write to IOMMU perf counter

bugzilla-daemon
2021-02-26T11:59:35Z

--- Comment #11 from David Coe (david.coe@live.co.uk) ---
Good morning again!

I've rebuilt the Ubuntu 20.10 kernel 5.8.0-44 overnight with increased delays.
Grep'ing dmesg for IOMMU gives:

20 msec delay:

[ 0.506947] pci 0000:00:00.2: AMD-Vi: Unable to read/write to IOMMU perf
counter.
[ 0.510822] pci 0000:00:00.2: AMD-Vi: Found IOMMU cap 0x40
[ 0.764160] AMD-Vi: AMD IOMMUv2 driver by Joerg Roedel <jroedel@suse.de>

30 & 40 msec delay:

[ 1.017676] pci 0000:00:00.2: AMD-Vi: IOMMU performance counters supported
[ 1.021591] pci 0000:00:00.2: AMD-Vi: Found IOMMU cap 0x40
[ 1.023053] perf/amd_iommu: Detected AMD IOMMU #0 (2 banks, 4
counters/bank).
[ 1.345196] AMD-Vi: AMD IOMMUv2 driver by Joerg Roedel <jroedel@suse.de>

At least on my 2400G platform, that suggests 20 msec is still too short. Of
course, YMMV :-).

Machines are grinding through the same trial on Ubuntu 21.04 alpha's 5.10.11
kernel and I'll post results in due course.

Best regards

David