[RFC PATCH] powerpc: Implement hotplug smt control

[Christophe Leroy]

Le 17/02/2022 à 08:04, Joel Stanley a écrit :
> x86 added a control for turning SMT on and off in commit 05736e4ac13c
> ("cpu/hotplug: Provide knobs to control SMT").
> 
> Implement this for powerpc as an alternative to the currently method of
> iterating through /sys/devices/system/cpu/cpuN/online for every CPU.
> 
>    # ppc64_cpu --info
>    Core   0:    0*    1*    2*    3*    4*    5*    6*    7*
>    Core   1:    8*    9*   10*   11*   12*   13*   14*   15*
>    # grep . /sys/devices/system/cpu/smt/*
>    /sys/devices/system/cpu/smt/active:1
>    /sys/devices/system/cpu/smt/control:on
>    # echo off > /sys/devices/system/cpu/smt/control
>    # ppc64_cpu --info
>    Core   0:    0*    1     2     3     4     5     6     7
>    Core   1:    8*    9    10    11    12    13    14    15
>    # grep . /sys/devices/system/cpu/smt/*
>    /sys/devices/system/cpu/smt/active:0
>    /sys/devices/system/cpu/smt/control:off
> 
> Signed-off-by: Joel Stanley <joel at jms.id.au>

Build fails with corenet64_smp_defconfig:

   CC      kernel/cpu.o
kernel/cpu.c: In function 'cpuhp_smt_disable':
kernel/cpu.c:2220:23: error: implicit declaration of function 
'cpu_down_maps_locked' [-Werror=implicit-function-declaration]
  2220 |                 ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
       |                       ^~~~~~~~~~~~~~~~~~~~
cc1: some warnings being treated as errors
make[1]: *** [scripts/Makefile.build:288: kernel/cpu.o] Error 1

Christophe