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
Status in linux package in Ubuntu:
In Progress
Bug description:
This boot warning (concealed by grub not taking over the fbcon console
on a solo installation but always present on a multi-boot) has been
bothering Linux users of AMD Ryzen machines for some time.
The problem is currently under discussion at kernel level
<https://bugzilla.kernel.org/show_bug.cgi?id=201753>.
One solution proposed by Suravee Suthikulpanit
<suravee.suthikulpa...@amd.com> <https://lkml.org/lkml/2021/2/8/486>
works but inserts a boot-up delay of (at least) 100 msec. A second
option by Alexander Monakov <amona...@ispras.ru>
<https://bugzilla.kernel.org/show_bug.cgi?id=201753> also works but
inserts no delay and more-or-less just moves one line of code.
I've tried both solutions with kernel rebuilds for both Breezy kernel
5.8.18 and Hirsute kernel 5.10.11 and both work on my AMD Ryzen 2400G.
Could I encourage your kernel experts to evaluate the situation (I
think SuSE folk already are).
My suggestion (as a humble user :-) ) would be to fold Alex's simple
patch into your own list of kernel tweeks and get the correction out
with the upcoming Hirsute release.
Best regards and all respect!
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