linux-kernel - Re: [PATCH 1/4] sched,time: count actually elapsed irq & softirq time

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Date:	Tue, 5 Jul 2016 16:00:54 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	mingo@...nel.org, pbonzini@...hat.com, fweisbec@...hat.com,
	wanpeng.li@...mail.com, efault@....de, tglx@...utronix.de,
	rkrcmar@...hat.com
Subject: Re: [PATCH 1/4] sched,time: count actually elapsed irq & softirq time

On Tue, Jul 05, 2016 at 09:08:16AM -0400, Rik van Riel wrote:
> On Tue, 2016-07-05 at 14:40 +0200, Frederic Weisbecker wrote:
> > On Thu, Jun 30, 2016 at 03:35:47PM -0400, riel@...hat.com wrote:
> > > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
> > > index 3d60e5d76fdb..018bae2ada36 100644
> > > --- a/kernel/sched/cputime.c
> > > +++ b/kernel/sched/cputime.c
> > > @@ -79,40 +79,50 @@ void irqtime_account_irq(struct task_struct
> > > *curr)
> > >  }
> > >  EXPORT_SYMBOL_GPL(irqtime_account_irq);
> > >  
> > > -static int irqtime_account_hi_update(void)
> > > +static cputime_t irqtime_account_hi_update(cputime_t maxtime)
> > >  {
> > >  	u64 *cpustat = kcpustat_this_cpu->cpustat;
> > >  	unsigned long flags;
> > > -	u64 latest_ns;
> > > -	int ret = 0;
> > > +	cputime_t irq_cputime;
> > >  
> > >  	local_irq_save(flags);
> > > -	latest_ns = this_cpu_read(cpu_hardirq_time);
> > > -	if (nsecs_to_cputime64(latest_ns) > cpustat[CPUTIME_IRQ])
> > > -		ret = 1;
> > > +	irq_cputime =
> > > nsecs_to_cputime(this_cpu_read(cpu_hardirq_time)) -
> > > +		      cpustat[CPUTIME_IRQ];
> > 
> > We might want to keep nsecs_to_cputime64(). If cputime_t == jiffies_t
> > == unsigned long,
> > we may have a problem after 49 days of interrupts. Arguably that's a
> > lot of IRQs
> > but lets be paranoid.
> 
> The macro nsecs_to_cputime64 is only defined in
> cputime_jiffies.h though, not in cputime_nsecs.h

Ah indeed.

> Want me to add a #define to the second file?

Yes please. It should be a simple cast.

Thanks!