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SubjectRe: [PATCH 4/5] irqtime: Move irqtime entry accounting after irq offset incrementation
On Tue, Dec 01, 2020 at 01:12:25AM +0100, Frederic Weisbecker wrote:
> +static s64 irqtime_get_delta(struct irqtime *irqtime)
> {
> + int cpu = smp_processor_id();
> s64 delta;
>
> delta = sched_clock_cpu(cpu) - irqtime->irq_start_time;
> irqtime->irq_start_time += delta;
>
> + return delta;
> +}
> +
> +/* Called after incrementing preempt_count on {soft,}irq_enter */
> +void irqtime_account_enter(struct task_struct *curr)
> +{
> + struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
> + u64 delta;
> +
> + if (!sched_clock_irqtime)
> + return;
> +
> + delta = irqtime_get_delta(irqtime);
> + /*
> + * 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.
> + */
> + if ((irq_count() == (SOFTIRQ_OFFSET | HARDIRQ_OFFSET)) &&
> + curr != this_cpu_ksoftirqd())
> + irqtime_account_delta(irqtime, delta, CPUTIME_SOFTIRQ);
> +}
> +
> +/* Called before decrementing preempt_count on {soft,}irq_exit */
> +void irqtime_account_exit(struct task_struct *curr)
> +{
> + struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
> + u64 delta;
> +
> + if (!sched_clock_irqtime)
> + return;
> +
> + delta = irqtime_get_delta(irqtime);
> /*
> * We do not account for softirq time from ksoftirqd here.
> * We want to continue accounting softirq time to ksoftirqd thread


Urgh...


Why not something like:

void irqtime_account_irq(struct task_struct *curr, unsigned int offset)
{
struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
unsigned int pc = preempt_count() - offset;
s64 delta;
int cpu;

if (!sched_clock_irqtime)
return;

cpu = smp_processor_id();
delta = sched_clock_cpu(cpu) - irqtime->irq_start_time;
irqtime->irq_start_time += delta;

/*
* 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.
*/
if (pc & HARDIRQ_MASK)
irqtime_account_delta(irqtime, delta, CPUTIME_IRQ);
else if ((pc & SOFTIRQ_OFFSET) && curr != this_cpu_ksoftirqd())
irqtime_account_delta(irqtime, delta, CPUTIME_SOFTIRQ);
}


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