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Subject: Re: [PATCH 5/6] Export ns irqtimes through /proc/stat -v1
From: Peter Zijlstra <peterz@infradead.org>
To: Venkatesh Pallipadi <venki@google.com>
Cc: Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        linux-kernel@vger.kernel.org, Paul Turner <pjt@google.com>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Shaun Ruffell <sruffell@digium.com>,
        Yong Zhang <yong.zhang0@gmail.com>
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Date: Tue, 26 Oct 2010 11:45:50 +0200
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On Mon, 2010-10-25 at 15:30 -0700, Venkatesh Pallipadi wrote:
> +static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
> +                                               struct rq *rq)
> +{
> +       cputime_t one_jiffy_scaled = cputime_to_scaled(cputime_one_jiffy);
> +       cputime64_t tmp = cputime_to_cputime64(cputime_one_jiffy);
> +       struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
> +
> +       if (irqtime_account_hi_update()) {
> +               cpustat->irq = cputime64_add(cpustat->irq, tmp);
> +       } else if (irqtime_account_si_update()) {
> +               cpustat->softirq = cputime64_add(cpustat->softirq, tmp);
> +       } else 

I'm still not sure about this else stmt, the above two conditions can
basically 'eat' user/system ticks. What we need to show is that there is
no bias towards either kind so the ratio is not affected -- can we make
such an argument?

>                if (user_tick) {
> +               account_user_time(p, cputime_one_jiffy, one_jiffy_scaled);
> +       } else if (p == rq->idle) {
> +               account_idle_time(cputime_one_jiffy);
> +       } else if (p->flags & PF_VCPU) { /* System time or guest time */
> +               account_guest_time(p, cputime_one_jiffy, one_jiffy_scaled);
> +       } else {
> +               __account_system_time(p, cputime_one_jiffy, one_jiffy_scaled,
> +                                       &cpustat->system);
> +       }
> +}