> On 28-Jun-2023, at 3:35 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. > Thanks for the patches Laurent. Is the SMT level retained even when dynamically changing SMT values? I am observing difference in behaviour with and without smt-enabled kernel command line option. When smt-enabled= option is specified SMT level is retained across cpu core remove and add. Without this option but changing SMT level during runtime using ppc64_cpu —smt=<level>, the SMT level is not retained after cpu core add. [root@ltcden8-lp8 ~]# ppc64_cpu —smt=4 [root@ltcden8-lp8 ~]# ppc64_cpu --info Core 0: 0* 1* 2* 3* 4 5 6 7 Core 1: 8* 9* 10* 11* 12 13 14 15 Core 2: 16* 17* 18* 19* 20 21 22 23 Core 3: 24* 25* 26* 27* 28 29 30 31 Remove a core, SMT level is retained. [root@ltcden8-lp8 ~]# ppc64_cpu --info Core 0: 0* 1* 2* 3* 4 5 6 7 Core 1: 8* 9* 10* 11* 12 13 14 15 Core 2: 16* 17* 18* 19* 20 21 22 23 [root@ltcden8-lp8 ~]# Add 3 cores, SMT level is not retained. [ 496.600648] Fallback order for Node 1: 1 0 [ 496.600655] Built 1 zonelists, mobility grouping on. Total pages: 1228159 [ 496.600676] Policy zone: Normal [ 496.661173] WARNING: workqueue cpumask: online intersect > possible intersect [ 499.530646] Fallback order for Node 3: 3 0 [ 499.530655] Built 2 zonelists, mobility grouping on. Total pages: 1228159 [ 499.530675] Policy zone: Normal ppc64_cpu --info Core 0: 0* 1* 2* 3* 4 5 6 7 Core 1: 8* 9* 10* 11* 12 13 14 15 Core 2: 16* 17* 18* 19* 20 21 22 23 Core 3: 24* 25* 26* 27* 28* 29* 30* 31* Core 4: 32* 33* 34* 35* 36* 37* 38* 39* Core 5: 40* 41* 42* 43* 44* 45* 46* 47* [root@ltcden8-lp8 ~]# - Sachin
