Le 05/07/2023 à 05:04, Zhang, Rui a écrit :

Hi, Laurent,

I want to test this patch set and found that it does not apply on top
of latest usptream git, because of some changes in this merge window,
so better rebase.

Hi Rui,

Thanks for your interest for this series.
The latest Thomas's changes came into the PowerPC next branch.
I'm working on a rebase.

Cheers,
Laurent.

thanks,
rui

On Thu, 2023-06-29 at 16:31 +0200, Laurent Dufour wrote:

quoted

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.

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@ellerman.id.au/ (local)
[2]
https://lore.kernel.org/linuxppc-dev/20230331153905.31698-1-ldufour@linux.ibm.com/ (local)

Laurent Dufour (1):
   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/bugs.c                    |   3 +-
  arch/x86/kernel/smpboot.c                     |   8 --
  include/linux/cpu.h                           |  25 +---
  include/linux/cpu_smt.h                       |  33 +++++
  kernel/cpu.c                                  | 118 ++++++++++++++--
--
  15 files changed, 187 insertions(+), 71 deletions(-)
  create mode 100644 include/linux/cpu_smt.h