Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM

Eric Dumazet
2010-12-10T17:18:26Z

Le vendredi 10 décembre 2010 à 14:47 +0100, Peter Zijlstra a écrit :
> Full patch..

> unt_system_vtime(struct task_struct *curr)
> {
> unsigned long flags;
> + s64 delta;
> int cpu;
> - u64 now, delta;
>
> if (!sched_clock_irqtime)
> return;
>
> local_irq_save(flags);
> -
> cpu = smp_processor_id();
> - now = sched_clock_cpu(cpu);
> - delta = now - per_cpu(irq_start_time, cpu);
> - per_cpu(irq_start_time, cpu) = now;
> - /*
> - * We do not account for softirq time from ksoftirqd here.
> - * We want to continue accounting softirq time to ksoftirqd thread
> - * in that case, so as not to confuse scheduler with a special task
> - * that do not consume any time, but still wants to run.
> - */
> + delta = sched_clock_cpu(cpu) - per_cpu(irq_start_time, cpu);
> + per_cpu(irq_start_time, cpu) += delta;

We should add some checkpatch warning to any new per_cpu() use.

delta = sched_clock_cpu(cpu) - __this_cpu_read(irq_start_time);
__this_cpu_add(irq_start_time, delta);

Also irq_time_write_begin() and irq_time_write_end() could be faster
(called for current cpu)

static inline void irq_time_write_begin(void)
{
__this_cpu_inc(irq_time_seq.sequence);
smp_wmb();
}

static inline void irq_time_write_end(void)
{
smp_wmb();
__this_cpu_inc(irq_time_seq.sequence);
}