[PATCH v3 0/9] Introduce SMT level and add PowerPC support

Laurent Dufour ldufour at linux.ibm.com
Fri Jun 30 23:41:24 AEST 2023

Le 30/06/2023 à 15:32, Sachin Sant a écrit :
>> On 29-Jun-2023, at 8:01 PM, Laurent Dufour <ldufour at linux.ibm.com> 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.
>> v3:
>>   Fix a build error in the patch 6/9
> Successfully tested the V3 version on a Power10 LPAR. Add/remove of
> processor core worked correctly, preserving the SMT level (on a kernel
> booted with smt-enabled= parameter)
> Laurent (Thanks!) also provided a patch to update the ppc64_cpu &
> lparstat utility. With patched ppc64_cpu utility verified that SMT level
> changed at runtime was preserved across processor core add (on
> a kernel booted without smt-enabled= parameter)
> Based on these test results
> Tested-by: Sachin Sant <sachinp at linux.ibm.com>

Thanks a lot, Sachin!

Once this series is accepted, I'll send the series to update ppc64_cpu.

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