Re: [PATCH 4/5] irqtime: Move irqtime entry accounting after irq offset incrementation

[Peter Zijlstra]

On Tue, Dec 01, 2020 at 03:35:45PM +0100, Frederic Weisbecker wrote:
> 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.

So the current tests get that all correct in a single function.
Splitting it out will just result in more lines to get wrong.

That is, I don't think you can do it saner than:

  account_softirq_enter() := irqtime_account_irq(curr, SOFTIRQ_OFFSET);
  account_softirq_exit()  := irqtime_account_irq(curr, 0);
  account_hardirq_enter() := irqtime_account_irq(curr, HARDIRQ_OFFSET);
  account_hardirq_exit()  := irqtime_account_irq(curr, 0);

Fundamentally you have to determine the previous context to determine
where to account the delta to. Note that when the previous context is
task context we throw away the delta.