Sachin Sant <sachinp@xxxxxxxxxxxxx> writes: >> 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. That's because ppc64_cpu is not using the sysfs SMT control file, it's just onlining/offlining threads manually. If you run: $ ppc64_cpu --smt=4 And then also do: $ echo 4 > /sys/devices/system/cpu/smt/control It should work as expected? ppc64_cpu will need to be updated to do that automatically. cheers
