Paul,
On 3/3/21 7:11 PM, Paul Menzel wrote:
This reverts commit 6778ff5b21bd8e78c8bd547fd66437cf2657fd9b.
The commit adds up to 100 ms to the boot process, which is not mentioned
in the commit message, and is making up more than 20 % on current
systems, where the Linux kernel takes 500 ms.
The 100 msec (5 * 20ms) is only for the worst-case scenario. For most cases,
the delay is not applicable. In addition, this patch has shown to fix the issue
for
some users in the field.
[ 0.000000] Linux version 5.11.0-10281-g19b4f3edd5c9
(root@a2ab663d937e) (gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU
Binutils for Debian) 2.35.1) #138 SMP Wed Feb 24 11:28:17 UTC 2021
[…]
[ 0.106422] smpboot: CPU0: AMD Ryzen 3 2200G with Radeon Vega Graphics
(family: 0x17, model: 0x11, stepping: 0x0)
[…]
[ 0.291257] pci 0000:00:00.2: AMD-Vi: Unable to read/write to IOMMU
perf counter.
[…]
Also, it does not fix the problem on an MSI B350M MORTAR with AMD Ryzen
3 2200G (even with ten retries, resulting in 200 ms time-out).
We are still investigating to root cause the long delay for the IOMMU
performance counter unit to disable power-gating, and allow access to
the performance counters. If your concern is the amount of retries,
we can try to reduce the number of retires.
[ 0.401152] pci 0000:00:00.2: AMD-Vi: Unable to read/write to IOMMU
perf counter.
Additionally, alternative proposed solutions [1] were not considered or
discussed.
[1]:https://lore.kernel.org/linux-iommu/alpine.lnx.2.20.13.2006030935570.3...@monopod.intra.ispras.ru/
This check has been introduced early on to detect a HW issue for certain
platforms in the past,
where the performance counters are not accessible and would result in silent
failure when try
to use the counters. This is considered legacy code, and can be removed if we
decide to no
longer provide sanity check for such case.
Regards,
Suravee
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