I'm taking over the series Michael sent previously [1] which is smartly
reviewing the initial series I sent [2]. This series is addressing the
comments sent by Thomas and me on the Michael's one.
Here is a short introduction to the issue this series is addressing:
When a new CPU is added, the kernel is activating all its threads. This
leads to weird, but functional, result when adding CPU on a SMT 4 system
for instance.
Here the newly added CPU 1 has 8 threads while the other one has 4 threads
active (system has been booted with the 'smt-enabled=4' kernel option):
ltcden3-lp12:~ # ppc64_cpu --info
Core 0: 0* 1* 2* 3* 4 5 6 7
Core 1: 8* 9* 10* 11* 12* 13* 14* 15*
This mixed SMT level may confused end users and/or some applications.
There is no SMT level recorded in the kernel (common code), neither in user
space, as far as I know. Such a level is helpful when adding new CPU or
when optimizing the energy efficiency (when reactivating CPUs).
When SMP and HOTPLUG_SMT are defined, this series is adding a new SMT level
(cpu_smt_num_threads) and few callbacks allowing the architecture code to
fine control this value, setting a max and a "at boot" level, and
controling whether a thread should be onlined or not.
v4:
Rebase on top of 6.5's updates
Remove a dependancy against the X86's symbol cpu_primary_thread_mask
v3:
Fix a build error in the patch 6/9
v2:
As Thomas suggested,
Reword some commit's description
Remove topology_smt_supported()
Remove topology_smt_threads_supported()
Introduce CONFIG_SMT_NUM_THREADS_DYNAMIC
Remove switch() in __store_smt_control()
Update kernel-parameters.txt
[1] https://lore.kernel.org/linuxppc-dev/20230524155630.794584-1-mpe@xxxxxxxxxxxxxx/
[2] https://lore.kernel.org/linuxppc-dev/20230331153905.31698-1-ldufour@xxxxxxxxxxxxx/
Laurent Dufour (2):
cpu/hotplug: remove dependancy against cpu_primary_thread_mask
cpu/SMT: Remove topology_smt_supported()
Michael Ellerman (8):
cpu/SMT: Move SMT prototypes into cpu_smt.h
cpu/SMT: Move smt/control simple exit cases earlier
cpu/SMT: Store the current/max number of threads
cpu/SMT: Create topology_smt_thread_allowed()
cpu/SMT: Allow enabling partial SMT states via sysfs
powerpc/pseries: Initialise CPU hotplug callbacks earlier
powerpc: Add HOTPLUG_SMT support
powerpc/pseries: Honour current SMT state when DLPAR onlining CPUs
.../ABI/testing/sysfs-devices-system-cpu | 1 +
.../admin-guide/kernel-parameters.txt | 4 +-
arch/Kconfig | 3 +
arch/powerpc/Kconfig | 2 +
arch/powerpc/include/asm/topology.h | 15 ++
arch/powerpc/kernel/smp.c | 8 +-
arch/powerpc/platforms/pseries/hotplug-cpu.c | 30 ++--
arch/powerpc/platforms/pseries/pseries.h | 2 +
arch/powerpc/platforms/pseries/setup.c | 2 +
arch/x86/include/asm/topology.h | 4 +-
arch/x86/kernel/cpu/common.c | 2 +-
arch/x86/kernel/smpboot.c | 8 -
include/linux/cpu.h | 25 +--
include/linux/cpu_smt.h | 33 ++++
kernel/cpu.c | 142 +++++++++++++-----
15 files changed, 196 insertions(+), 85 deletions(-)
create mode 100644 include/linux/cpu_smt.h
--
2.41.0
