Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1428232

Re: [PATCH 1/5] sched,time: count actually elapsed irq & softirq time

Show all headers | View raw

[Multipart message — attachments visible in raw view] - view raw

On Tue, 2016-06-21 at 23:21 +0200, Peter Zijlstra wrote:
> On Thu, Jun 16, 2016 at 12:06:03PM -0400, riel@redhat.com wrote:
> > 
> > +static unsigned long irqtime_account_hi_update(unsigned long
> > max_jiffies)
> >  {
> >  	u64 *cpustat = kcpustat_this_cpu->cpustat;
> > +	unsigned long irq_jiffies;
> >  	unsigned long flags;
> > +	u64 irq;
> >  
> >  	local_irq_save(flags);
> > +	irq = this_cpu_read(cpu_hardirq_time) -
> > cpustat[CPUTIME_IRQ];
> > +	irq_jiffies = min(cputime_to_jiffies(irq), max_jiffies);
> cputime_to_jiffies is a division, could we not avoid that by doing
> something like:
> 
> 	irq_jiffies = min(irq, jiffies_to_cputime(max_jiffies));
> 	while (irq_jiffies > cputime_one_jiffy) {
> 		irq_jiffies -= cputime_one_jiffy;
> 		cpustat[CPUTIME_IRQ] += cputime_one_jiffy;
> 	}
> 
> assuming that the loop is 'rare' etc.. If not, only do the division
> on
> that same > cputime_one_jiffy condition.

I suspect the loop is not rare on systems with nohz_idle,
where it may be quite a while before a timer tick happens
on an idle cpu.

I can certainly make sure the division is only done when
irq > 2*cputime_one_jiffy. I will do that in the next
version.

-- 
All Rights Reversed.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 1/5] sched,time: count actually elapsed irq & softirq time riel@redhat.com - 2016-06-16 18:10 +0200
  Re: [PATCH 1/5] sched,time: count actually elapsed irq & softirq time kbuild test robot <lkp@intel.com> - 2016-06-16 18:30 +0200
  Re: [PATCH 1/5] sched,time: count actually elapsed irq & softirq time Peter Zijlstra <peterz@infradead.org> - 2016-06-21 23:30 +0200
    Re: [PATCH 1/5] sched,time: count actually elapsed irq & softirq  time Rik van Riel <riel@redhat.com> - 2016-06-22 00:30 +0200
    Re: [PATCH 1/5] sched,time: count actually elapsed irq & softirq time Paolo Bonzini <pbonzini@redhat.com> - 2016-06-22 12:50 +0200
      Re: [PATCH 1/5] sched,time: count actually elapsed irq & softirq time Peter Zijlstra <peterz@infradead.org> - 2016-06-22 13:00 +0200

csiph-web