Commit ba2591a5 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

sched/smt: Update sched_smt_present at runtime 



The static key sched_smt_present is only updated at boot time when SMT
siblings have been detected. Booting with maxcpus=1 and bringing the
siblings online after boot rebuilds the scheduling domains correctly but
does not update the static key, so the SMT code is not enabled.

Let the key be updated in the scheduler CPU hotplug code to fix this.

Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
parent 56563f53

kernel/sched/core.c

+12 −18
Original line number Diff line number Diff line
@@ -5777,6 +5777,18 @@ int sched_cpu_activate(unsigned int cpu) 
	struct rq *rq = cpu_rq(cpu);

	struct rq_flags rf;



#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.

	 */

	if (cpumask_weight(cpu_smt_mask(cpu)) > 1)

		static_branch_enable_cpuslocked(&sched_smt_present);

#endif

	set_cpu_active(cpu, true);



	if (sched_smp_initialized) {
@@ -5874,22 +5886,6 @@ int sched_cpu_dying(unsigned int cpu) 
}

#endif



#ifdef CONFIG_SCHED_SMT

DEFINE_STATIC_KEY_FALSE(sched_smt_present);



static void sched_init_smt(void)

{

	/*

	 * We've enumerated all CPUs and will assume that if any CPU

	 * has SMT siblings, CPU0 will too.

	 */

	if (cpumask_weight(cpu_smt_mask(0)) > 1)

		static_branch_enable(&sched_smt_present);

}

#else

static inline void sched_init_smt(void) { }

#endif



void __init sched_init_smp(void)

{

	sched_init_numa();
@@ -5911,8 +5907,6 @@ void __init sched_init_smp(void) 
	init_sched_rt_class();

	init_sched_dl_class();



	sched_init_smt();



	sched_smp_initialized = true;

}

kernel/sched/fair.c

+1 −0
Original line number Diff line number Diff line
@@ -6238,6 +6238,7 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p 
}



#ifdef CONFIG_SCHED_SMT

DEFINE_STATIC_KEY_FALSE(sched_smt_present);



static inline void set_idle_cores(int cpu, int val)

{

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