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sched/smt: Update sched_smt_present at runtime 

commit ba2591a599 upstream

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: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
pull/10/head
Peter Zijlstra 2018-05-29 16:43:46 +02:00 committed by Greg Kroah-Hartman
parent 202f905608
commit fc890e9b57
2 changed files with 13 additions and 18 deletions
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30
kernel/sched/core.c
View File

@ -5615,6 +5615,18 @@ 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) {
@ -5710,22 +5722,6 @@ 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)
{
cpumask_var_t non_isolated_cpus;
@ -5755,8 +5751,6 @@ void __init sched_init_smp(void)
init_sched_rt_class();
init_sched_dl_class();
sched_init_smt();
sched_smp_initialized = true;
}

1
kernel/sched/fair.c
View File

@ -5631,6 +5631,7 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
}
#ifdef CONFIG_SCHED_SMT
DEFINE_STATIC_KEY_FALSE(sched_smt_present);
static inline void set_idle_cores(int cpu, int val)
{