Re: [PATCH v4 00/10] Introduce SMT level and add PowerPC support

[Laurent Dufour]

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@xxxxxxxxx>

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@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