Hi Alex!
Herewith a summary of our accumulated results [1] for Surajee's IOMMU
patch using 20 msecs wait and logged retries on AMD's Ryzen:
Ryzen Kernel Cold Warm
4700U 5.11.0-11 6 1
3500U 5.11.7 5 6
2500U 5.8.0-45 5
5.12.0 RC3 5 > 5
2400G 5.11.0-11 6 6
5.8.0-45 5 6
2200G ? >10
Two points are clear:
1. there are differences between cold and warm boot, mostly marginal but
marked and very consistent with the quite new 4700U.
2. the choice of 5 as the maximum retry number is unfortunate. Mostly,
it guarantees all our Ryzens just fail the IOMMU write test!
The 2200G is a bit of a odd-ball and it's owner, understandably, wants a
more elegant solution than just upping the number of retries. For the
rest of us, a maximum of 6 or 7 would sort it.
Best regards and many thanks
David
[1] https://bugzilla.kernel.org/show_bug.cgi?id=201753
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https://bugs.launchpad.net/bugs/1917203
Title:
AMD-Vi: Unable to read/write to IOMMU perf counter
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