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    SubjectRe: [PATCH v4 00/10] Introduce SMT level and add PowerPC support
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    Le 09/07/2023 à 17:25, Zhang, Rui a écrit :
    > Hi, Laurent,
    >
    > I ran into a boot hang regression with latest upstream code, and it
    > took me a while to bisect the offending commit and workaround it.
    >
    > Now I have tested this patch series on an Intel RaptorLake Hybrid
    > platform (4 Pcores with HT and 4 Ecores without HT), and it works as
    > expected.
    >
    > So, for patch 1~7 in this series,
    >
    > Tested-by: Zhang Rui <rui.zhang@intel.com>

    Thanks Rui!

    > thanks,
    > rui
    >
    > On Wed, 2023-07-05 at 16:51 +0200, Laurent Dufour wrote:
    >> 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@ellerman.id.au/
    >> [2]
    >> https://lore.kernel.org/linuxppc-dev/20230331153905.31698-1-ldufour@linux.ibm.com/
    >>
    >>
    >> 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
    >>
    >

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