Comment 10 for bug 1917203

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