Re: [PATCH 3/7] Add IRQ_TIME_ACCOUNTING, finer accounting of irq time -v3

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2010-09-30 at 13:38 -0700, Venkatesh Pallipadi wrote:
> On Thu, Sep 30, 2010 at 9:29 AM, Venkatesh Pallipadi <venki@google.com> wrote:
> > On Thu, Sep 30, 2010 at 4:06 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >> On Wed, 2010-09-29 at 12:21 -0700, Venkatesh Pallipadi wrote:
> >>> +void account_system_vtime(struct task_struct *curr)
> >>> +{
> >>> +       unsigned long flags;
> >>> +       int cpu;
> >>> +       u64 now, delta;
> >>> +
> >>> +       if (!sched_clock_irqtime)
> >>> +               return;
> >>> +
> >>> +       local_irq_save(flags);
> >>> +
> >>> +       now = sched_clock();
> >>> +       cpu = smp_processor_id();
> >>
> >> Like said before, that really wants to read like:
> >>
> >>        cpu = smp_processor_id();
> >>        now = sched_clock_cpu(cpu);
> >>
> >> sched_clock() is raw tsc + ns conversion and can go all over the place.
> >
> > sched_clock_cpu() won't really work for here, due to what looks like
> > idle and timer tick dependencies. Using sched_clock_cpu(), I end up
> > accounting CPU idle time to hardirq due to time captured before the
> > handler and after the handler.
> >
> 
> Specifically, here is the now and delta log from my test setup with
> using sched_clock_cpu() above (data below from a particular CPU)
> 
>           <idle>-0     [001]  1697.910060: account_system_vtime:
> SOFTIRQ STOP 1700897011613, delta 3555
>           <idle>-0     [001]  1697.911047: account_system_vtime: IRQ
> START 1700897999028

Dude, linewrap hell! And what are you trying to illustrate?