> On 29-Jun-2023, at 8:01 PM, Laurent Dufour <ldufour@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> - Sachin
