4.19-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra (Intel) peterz@infradead.org
commit c5511d03ec090980732e929c318a7a6374b5550e upstream
Currently the 'sched_smt_present' static key is enabled when at CPU bringup SMT topology is observed, but it is never disabled. However there is demand to also disable the key when the topology changes such that there is no SMT present anymore.
Implement this by making the key count the number of cores that have SMT enabled.
In particular, the SMT topology bits are set before interrrupts are enabled and similarly, are cleared after interrupts are disabled for the last time and the CPU dies.
Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Ingo Molnar mingo@kernel.org Cc: Andy Lutomirski luto@kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Jiri Kosina jkosina@suse.cz Cc: Tom Lendacky thomas.lendacky@amd.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: David Woodhouse dwmw@amazon.co.uk Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Andi Kleen ak@linux.intel.com Cc: Dave Hansen dave.hansen@intel.com Cc: Casey Schaufler casey.schaufler@intel.com Cc: Asit Mallick asit.k.mallick@intel.com Cc: Arjan van de Ven arjan@linux.intel.com Cc: Jon Masters jcm@redhat.com Cc: Waiman Long longman9394@gmail.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Dave Stewart david.c.stewart@intel.com Cc: Kees Cook keescook@chromium.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20181125185004.246110444@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/core.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5741,15 +5741,10 @@ int sched_cpu_activate(unsigned int cpu)
#ifdef CONFIG_SCHED_SMT /* - * The sched_smt_present static key needs to be evaluated on every - * hotplug event because at boot time SMT might be disabled when - * the number of booted CPUs is limited. - * - * If then later a sibling gets hotplugged, then the key would stay - * off and SMT scheduling would never be functional. + * When going up, increment the number of cores with SMT present. */ - if (cpumask_weight(cpu_smt_mask(cpu)) > 1) - static_branch_enable_cpuslocked(&sched_smt_present); + if (cpumask_weight(cpu_smt_mask(cpu)) == 2) + static_branch_inc_cpuslocked(&sched_smt_present); #endif set_cpu_active(cpu, true);
@@ -5793,6 +5788,14 @@ int sched_cpu_deactivate(unsigned int cp */ synchronize_rcu_mult(call_rcu, call_rcu_sched);
+#ifdef CONFIG_SCHED_SMT + /* + * When going down, decrement the number of cores with SMT present. + */ + if (cpumask_weight(cpu_smt_mask(cpu)) == 2) + static_branch_dec_cpuslocked(&sched_smt_present); +#endif + if (!sched_smp_initialized) return 0;