"Gautham R. Shenoy" [off-list ref] writes:

From: "Gautham R. Shenoy" <redacted>

Currently on PSeries Linux guests, the offlined CPU can be put to one
of the following two states:
   - Long term processor cede (also called extended cede)
   - Returned to the hypervisor via RTAS "stop-self" call.

This is controlled by the kernel boot parameter "cede_offline=on/off".

By default the offlined CPUs enter extended cede. The PHYP hypervisor
considers CPUs in extended cede to be "active" since they are still
under the control fo the Linux guests. Hence, when we change the SMT
modes by offlining the secondary CPUs, the PURR and the RWMR SPRs will
continue to count the values for offlined CPUs in extended cede as if
they are online. This breaks the accounting in tools such as lparstat.

To fix this, ensure that by default the offlined CPUs are returned to
the hypervisor via RTAS "stop-self" call by changing the default value
of "cede_offline_enabled" to false.

Fixes: commit 3aa565f53c39 ("powerpc/pseries: Add hooks to put the CPU
into an appropriate offline state")

Signed-off-by: Gautham R. Shenoy <redacted>

I'm OK with changing the default as a precursor to removing the code
that implements the cede offline mode.

Acked-by: Nathan Lynch <redacted>