On Tue, Dec 01, 2020 at 02:34:49PM +0100, Thomas Gleixner wrote:
> On Tue, Dec 01 2020 at 12:40, Frederic Weisbecker wrote:
> > On Tue, Dec 01, 2020 at 12:33:26PM +0100, Thomas Gleixner wrote:
> >> > /*
> >> > * 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);
> >> > }
> >>
> >> Why not making all of this explicit instead of these conditionals?
> >
> > Hmm, I'm not sure I get what you suggest?
>
> Instead of playing games with preeempt count and offsets and checking
> for ksoftirqd, can't you just have:
>
> account_hardirqtime()
> account_softirqtime()
>
> and call them from the right spots. See the below for illustration (it's
> obviously incomplete).
>
> Thanks,
>
> tglx
> ---
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -377,6 +377,7 @@ static inline void invoke_softirq(void)
> return;
>
> if (!force_irqthreads) {
> + account_softirq_enter_time(current);
> #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
> /*
> * We can safely execute softirq on the current stack if
> @@ -391,6 +392,7 @@ static inline void invoke_softirq(void)
> * to prevent from any overrun.
> */
> do_softirq_own_stack();
> + account_softirq_exit_time(current);
Indeed for the softirq part it simplifies things.
> #endif
> } else {
> wakeup_softirqd();
> @@ -417,7 +419,7 @@ static inline void __irq_exit_rcu(void)
> #else
> lockdep_assert_irqs_disabled();
> #endif
> - account_irq_exit_time(current);
> + account_hardirq_exit_time(current);
And that one too makes things simple. But note that
account_hardirq_enter_time()
will still need some preempt count checks to see if
this is a nested hardirq, a hardirq interrupting a softirq
or a hardirq interrupting a task.
But I think it's a win in the end. I'll try that.
Thanks.
> preempt_count_sub(HARDIRQ_OFFSET);
> if (!in_interrupt() && local_softirq_pending())
> invoke_softirq();
