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sched/smt: Make sched_smt_present track topology
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
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@ -5738,15 +5738,10 @@ int sched_cpu_activate(unsigned int cpu)
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#ifdef CONFIG_SCHED_SMT
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#ifdef CONFIG_SCHED_SMT
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/*
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/*
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* The sched_smt_present static key needs to be evaluated on every
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* When going up, increment the number of cores with SMT present.
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* hotplug event because at boot time SMT might be disabled when
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* the number of booted CPUs is limited.
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*
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* If then later a sibling gets hotplugged, then the key would stay
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* off and SMT scheduling would never be functional.
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*/
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*/
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if (cpumask_weight(cpu_smt_mask(cpu)) > 1)
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if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
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static_branch_enable_cpuslocked(&sched_smt_present);
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static_branch_inc_cpuslocked(&sched_smt_present);
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#endif
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#endif
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set_cpu_active(cpu, true);
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set_cpu_active(cpu, true);
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@ -5790,6 +5785,14 @@ int sched_cpu_deactivate(unsigned int cpu)
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*/
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*/
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synchronize_rcu_mult(call_rcu, call_rcu_sched);
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synchronize_rcu_mult(call_rcu, call_rcu_sched);
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#ifdef CONFIG_SCHED_SMT
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/*
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* When going down, decrement the number of cores with SMT present.
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*/
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if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
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static_branch_dec_cpuslocked(&sched_smt_present);
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#endif
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if (!sched_smp_initialized)
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if (!sched_smp_initialized)
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return 0;
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return 0;
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