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SubjectRe: [PATCH 4/5] irqtime: Move irqtime entry accounting after irq offset incrementation
On Tue, Dec 01, 2020 at 10:20:11AM +0100, Peter Zijlstra wrote:
> 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);
> }
>
>

Right that's better, I'll do that.

Thanks.

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