Hi Alex!
A splendidly prompt piece of cherry-picking. Many thanks.
I've checked your test release on my Ryzen 2400G on current Ubuntu 20.10 and it
still gives the diagostic:
AMD-Vi: Unable to read/write to IOMMU perf counter
It's to be expected! The little crew engaged with testing Suravee
Suthikulpanit's patch [1] are finding that the 2400G (that's me) needs
120 msec for power-gating and the 2200G (that's Paul Menzel] needs >200
msecs. Suravee's RFC v3 provides 5 x 20 msecs delay which just isn't
enough for these lesser Ryzen's :-).
If you change Suravee's patch line
for (retry = 5; retry; retry--) {
to
for (retry = 25; retry; retry--) {
all will be well (imho). The maximum delay is indeed outrageous but only
that really necessary to enable IOMMU is actually used. Eventually a
proper solution will be found (in firmware or silicon) but (unlike at
present) the many users of entry-level Ryzen CPU's will not have their
IOMMU crippled during linux boot-up.
Incidentally, if you do rebuild your (very kind) test-release with the
above change (please, please), could you also include the deb package
for linux-tools for the same kernel. Things like the command "perf stat
-a -e amd_iommu/mem_trans_total/ test" (used to test IOMMU performance
in user-space) are tied to the running kernel-version and will then
work.
Best regards and again many thanks
David
[1] https://bugzilla.kernel.org/show_bug.cgi?id=201753
** Bug watch added: Linux Kernel Bug Tracker #201753
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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