Selectively block cores from the scheduler with sysctl hw.blockcpu
by from OpenBSD Journal on (#74YPK)
We're a little late reporting it but...
The familiar safeguardsysctl hw.smtis now deprecated,having been replaced by a more flexible mechanismwhich allows discriminating between different varieties of core type.
First, Theo de Raadt (deraadt@) enabled the mechanism for OpenBSD/amd64 in thiscommit:
CVSROOT:/cvsModule name:srcChanges by:deraadt@cvs.openbsd.org2026/03/31 10:46:22Modified files:sys/sys : sched.h sysctl.h sys/kern : kern_sched.c kern_sysctl.c sys/arch/amd64/amd64: identcpu.c machdep.c sys/arch/amd64/include: cpu.h lib/libc/sys : sysctl.2 Log message:Some new intel machines have a new 3rd tier of cpus called LP-E which areE-core (Atom) without L3 cache. These v are Lethargic, and it suckswhen processes migrate to them.