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Description of problem: Modern POWER CPUs support hardware multi-threading (similar to hyperthreading on x86) - up to 4 threads on POWER7 and up to 8 threads on POWER8. Which threading mode gives the best performance can vary with the workload. Therefore depending on the system's typical workload it might be useful to have it default to a particular threading mode on boot. The ppc64_cpu tool included in the powerpc-utils package allows the threading mode to be changed at runtime (for both bare metal systems, and PowerVM or KVM guests), but there's no convenient config file to set the mode which will be used at boot, meaning the kernel will always default to the maximum number of threads. We should add a configuration file and init scripts which allows the default threading mode for a newly booted system to be chosen. Additional info: Note that the qemu-kvm-rhev package currently installs configuration to force SMT off (i.e. 1 thread per core) this is necessary in order to run KVM guests. Whatever method we use for general configuration will need to work with that.
David, do you have a similar issue opened against upstream powerpc-utils? If so, could you please provide a link here?
it's fixed in powerpc-utils-1.3.4-11.el7
Verified with powerpc-utils-1.3.4-14.el7 in RHEL 7.9 [root@ibm-p8-01-lp2 ~]# cat /etc/redhat-release Red Hat Enterprise Linux Server release 7.9 Beta (Maipo) [root@ibm-p8-01-lp2 ~]# rpm -q kernel powerpc-utils kernel-3.10.0-1150.el7.ppc64le powerpc-utils-1.3.4-14.el7.ppc64le [root@ibm-p8-01-lp2 ~]# ppc64_cpu --smt SMT=8 [root@ibm-p8-01-lp2 ~]# rpm -ql powerpc-utils | grep systemd /usr/lib/systemd/system/smt_off.service [root@ibm-p8-01-lp2 ~]# systemctl enable smt_off.service Created symlink from /etc/systemd/system/multi-user.target.wants/smt_off.service to /usr/lib/systemd/system/smt_off.service. [root@ibm-p8-01-lp2 ~]# reboot ... [root@ibm-p8-01-lp2 ~]# systemctl status smt_off.service ● smt_off.service - ppc64 set SMT off Loaded: loaded (/usr/lib/systemd/system/smt_off.service; enabled; vendor preset: disabled) Active: active (exited) since Thu 2020-06-18 12:27:26 EDT; 39s ago Process: 1096 ExecStart=/usr/sbin/ppc64_cpu --smt=off (code=exited, status=0/SUCCESS) Main PID: 1096 (code=exited, status=0/SUCCESS) CGroup: /system.slice/smt_off.service Jun 18 12:27:26 ibm-p8-01-lp2.khw1.lab.eng.bos.redhat.com systemd[1]: Startin... Jun 18 12:27:26 ibm-p8-01-lp2.khw1.lab.eng.bos.redhat.com systemd[1]: Started... Hint: Some lines were ellipsized, use -l to show in full. [root@ibm-p8-01-lp2 ~]# ppc64_cpu --smt SMT is off [root@ibm-p8-01-lp2 ~]# systemctl disable smt_off.service Removed symlink /etc/systemd/system/multi-user.target.wants/smt_off.service. [root@ibm-p8-01-lp2 ~]# reboot ... [root@ibm-p8-01-lp2 ~]# systemctl status smt_off.service ● smt_off.service - ppc64 set SMT off Loaded: loaded (/usr/lib/systemd/system/smt_off.service; disabled; vendor preset: disabled) Active: inactive (dead) [root@ibm-p8-01-lp2 ~]# ppc64_cpu --smt SMT=8
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (powerpc-utils bug fix and enhancement update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2020:3893