powerpc/64: Remove PPC64 special case for cputime accounting default

Distro kernels tend to be moving to VIRT_CPU_ACCOUNTING_GEN, and there
is not much reason why PPC64 should be special here. Remove the special
case and make the ppc64 and pseries defconfigs use GEN accounting
(others will use TICK, as-per Kconfig defaults).

VIRT_CPU_ACCOUNTING_NATIVE does provide scaled vtime and stolen time
apportioned between system and user time, and vtime accounting is not
unconditionally enabled, and possibly other things. But it would be
better at this point to extend GEN to cover important missing features
rather than directing users back to a less used option.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220902085316.2071519-4-npiggin@gmail.com

arch/powerpc/configs/ppc64_defconfig

@@ -1,7 +1,9 @@
 CONFIG_SYSVIPC=y
 CONFIG_POSIX_MQUEUE=y
+# CONFIG_CONTEXT_TRACKING_USER_FORCE is not set
 CONFIG_NO_HZ=y
 CONFIG_HIGH_RES_TIMERS=y
+CONFIG_VIRT_CPU_ACCOUNTING_GEN=y
 CONFIG_TASKSTATS=y
 CONFIG_TASK_DELAY_ACCT=y
 CONFIG_IKCONFIG=y

arch/powerpc/configs/pseries_defconfig

@@ -3,8 +3,10 @@ CONFIG_NR_CPUS=2048
 CONFIG_SYSVIPC=y
 CONFIG_POSIX_MQUEUE=y
 CONFIG_AUDIT=y
+# CONFIG_CONTEXT_TRACKING_USER_FORCE is not set
 CONFIG_NO_HZ=y
 CONFIG_HIGH_RES_TIMERS=y
+CONFIG_VIRT_CPU_ACCOUNTING_GEN=y
 CONFIG_TASKSTATS=y
 CONFIG_TASK_DELAY_ACCT=y
 CONFIG_TASK_XACCT=y

init/Kconfig

@@ -461,8 +461,7 @@ config VIRT_CPU_ACCOUNTING
 
 choice
 	prompt "Cputime accounting"
-	default TICK_CPU_ACCOUNTING if !PPC64
-	default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
+	default TICK_CPU_ACCOUNTING
 
 # Kind of a stub config for the pure tick based cputime accounting
 config TICK_CPU_ACCOUNTING