Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28

From	Jesper Dangaard Brouer <brouer@redhat.com>
Newsgroups	linux.kernel
Subject	Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28
Date	2017-03-28 15:30 +0200
Message-ID	<tpZma-8cB-35@gated-at.bofh.it> (permalink)
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On Tue, 28 Mar 2017 15:06:04 +0200
Frederic Weisbecker <fweisbec@gmail.com> wrote:

> On Tue, Mar 28, 2017 at 02:26:42PM +0200, Peter Zijlstra wrote:
> > On Tue, Mar 28, 2017 at 06:34:52PM +0800, Wanpeng Li wrote:  
> > > 
> > > sched_clock_cpu(cpu) should be converted from cputime to ns.  
> > 
> > Uhm, no. sched_clock_cpu() returns u64 in ns.  
> 
> Yes, and most of the cputime_t have been converted to u64 so there
> should be no such conversion issue between u64 and cputime_t anymore.
> 
> Perhaps my commit has another side effect on softirq time accounting,
> I'll see if I can reproduce.

(Disclaimer without knowing anything about the scheduler code)
my theory is that irqtime_account_irq() does not get invoked often
enough, as in my pktgen "overload" use-case keeps softirq always
running. And your change moved updating cpustat[CPUTIME_SOFTIRQ] here.
Before it got updated by account_other_time() which gets invoked from
irqtime_account_process_tick().

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

Thread

Bisected softirq accounting issue in v4.11-rc1~170^2~28 Jesper Dangaard Brouer <brouer@redhat.com> - 2017-03-28 10:20 +0200
  Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Wanpeng Li <kernellwp@gmail.com> - 2017-03-28 12:40 +0200
    Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Jesper Dangaard Brouer <brouer@redhat.com> - 2017-03-28 14:00 +0200
    Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Peter Zijlstra <peterz@infradead.org> - 2017-03-28 14:30 +0200
      Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Frederic Weisbecker <fweisbec@gmail.com> - 2017-03-28 15:10 +0200
        Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Jesper Dangaard Brouer <brouer@redhat.com> - 2017-03-28 15:30 +0200
  Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Frederic Weisbecker <fweisbec@gmail.com> - 2017-03-28 16:40 +0200
    Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Jesper Dangaard Brouer <brouer@redhat.com> - 2017-03-28 17:30 +0200
      Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Frederic Weisbecker <fweisbec@gmail.com> - 2017-03-28 23:20 +0200
        Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Jesper Dangaard Brouer <brouer@redhat.com> - 2017-03-29 11:40 +0200
          Re: Bisected softirq accounting issue in v4.11-rc1~170^2~28 Frederic Weisbecker <fweisbec@gmail.com> - 2017-03-29 15:20 +0200

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