Sebastian, This patch removes the raw spinlock operations when updating cputtime in the vtime_* functions in kernel/sched/cputime.c.
Based on Frederic's commit b7ce2277f087fd052, there is no need for the raw spinlocks in vtime_* functions to guard against writer concurrency and the RT versions of write_seqcount_begin() and write_seqcount_end() make calls to preempt_disable_rt() and preempt_enable_rt(), so we'll be in atomic context while updating cputime. I've run this patch on x86_64 4.4.6-rt14 and the RHEL-RT kernel, with 12h rteval runs on systems with both no tuning and systems with isolcpus/rcu_nocbs/nohz_full cpus. No ill effects seen. Signed-off-by: Rik van Riel <r...@redhat.com> Signed-off-by: Clark Williams <willi...@redhat.com> --- kernel/sched/cputime.c | 18 ------------------ 1 file changed, 18 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 0f75a38cff96..9a823ced7e4a 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -696,45 +696,37 @@ static void __vtime_account_system(struct task_struct *tsk) void vtime_account_system(struct task_struct *tsk) { - raw_spin_lock(&tsk->vtime_lock); write_seqcount_begin(&tsk->vtime_seq); __vtime_account_system(tsk); write_seqcount_end(&tsk->vtime_seq); - raw_spin_unlock(&tsk->vtime_lock); } void vtime_gen_account_irq_exit(struct task_struct *tsk) { - raw_spin_lock(&tsk->vtime_lock); write_seqcount_begin(&tsk->vtime_seq); __vtime_account_system(tsk); if (context_tracking_in_user()) tsk->vtime_snap_whence = VTIME_USER; write_seqcount_end(&tsk->vtime_seq); - raw_spin_unlock(&tsk->vtime_lock); } void vtime_account_user(struct task_struct *tsk) { cputime_t delta_cpu; - raw_spin_lock(&tsk->vtime_lock); write_seqcount_begin(&tsk->vtime_seq); delta_cpu = get_vtime_delta(tsk); tsk->vtime_snap_whence = VTIME_SYS; account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu)); write_seqcount_end(&tsk->vtime_seq); - raw_spin_unlock(&tsk->vtime_lock); } void vtime_user_enter(struct task_struct *tsk) { - raw_spin_lock(&tsk->vtime_lock); write_seqcount_begin(&tsk->vtime_seq); __vtime_account_system(tsk); tsk->vtime_snap_whence = VTIME_USER; write_seqcount_end(&tsk->vtime_seq); - raw_spin_unlock(&tsk->vtime_lock); } void vtime_guest_enter(struct task_struct *tsk) @@ -746,23 +738,19 @@ void vtime_guest_enter(struct task_struct *tsk) * synchronization against the reader (task_gtime()) * that can thus safely catch up with a tickless delta. */ - raw_spin_lock(&tsk->vtime_lock); write_seqcount_begin(&tsk->vtime_seq); __vtime_account_system(tsk); current->flags |= PF_VCPU; write_seqcount_end(&tsk->vtime_seq); - raw_spin_unlock(&tsk->vtime_lock); } EXPORT_SYMBOL_GPL(vtime_guest_enter); void vtime_guest_exit(struct task_struct *tsk) { - raw_spin_lock(&tsk->vtime_lock); write_seqcount_begin(&tsk->vtime_seq); __vtime_account_system(tsk); current->flags &= ~PF_VCPU; write_seqcount_end(&tsk->vtime_seq); - raw_spin_unlock(&tsk->vtime_lock); } EXPORT_SYMBOL_GPL(vtime_guest_exit); @@ -775,30 +763,24 @@ void vtime_account_idle(struct task_struct *tsk) void arch_vtime_task_switch(struct task_struct *prev) { - raw_spin_lock(&prev->vtime_lock); write_seqcount_begin(&prev->vtime_seq); prev->vtime_snap_whence = VTIME_SLEEPING; write_seqcount_end(&prev->vtime_seq); - raw_spin_unlock(&prev->vtime_lock); - raw_spin_lock(¤t->vtime_lock); write_seqcount_begin(¤t->vtime_seq); current->vtime_snap_whence = VTIME_SYS; current->vtime_snap = sched_clock_cpu(smp_processor_id()); write_seqcount_end(¤t->vtime_seq); - raw_spin_unlock(¤t->vtime_lock); } void vtime_init_idle(struct task_struct *t, int cpu) { unsigned long flags; - raw_spin_lock_irqsave(&t->vtime_lock, flags); write_seqcount_begin(&t->vtime_seq); t->vtime_snap_whence = VTIME_SYS; t->vtime_snap = sched_clock_cpu(cpu); write_seqcount_end(&t->vtime_seq); - raw_spin_unlock_irqrestore(&t->vtime_lock, flags); } cputime_t task_gtime(struct task_struct *t) -- 2.5.5
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