Comment 100 for bug 1690085

(In reply to James Le Cuirot from comment #13)
> (In reply to fin4478 from comment #12)
> > With RCU_NOCB_CPU you need to have the following in the kernel command
> line:
> > rcu_nocbs=0-11
>
> Correct, there used to be CONFIG_RCU_NOCB_CPU_ALL until very recently. I
> don't know why it was removed. I still see this as a workaround though as I
> gather it effectively avoids C6.
>

RCU_NOCB_CPU_ALL was removed 2017-06-08 18:52:43 -0700. "The CONFIG_RCU_NOCB_CPU_ALL, CONFIG_RCU_NOCB_CPU_NONE, and
CONFIG_RCU_NOCB_CPU_ZERO Kconfig options are used only in testing and
are redundant with the rcu_nocbs= boot parameter. This commit therefore
removes these three Kconfig options and adjusts the rcutorture scripts
to use the boot parameter instead."

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/init/Kconfig?h=v4.14-rc3&id=44c65ff2e3b0b48250a970183ab53b0602c25764

This is typical not end user friendly solution from tired programmers. Other companies have a conspiracy against Amd, they do want to make Amd look bad and do code like this. Another example, Ryzen k10temp and Zen cpu select patches have been ready for several months but are not in the mainline kernel. Coffee lake and q cpus are coming.