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

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Date:	Thu, 30 Sep 2010 09:29:22 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org, Paul Turner <pjt@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH 3/7] Add IRQ_TIME_ACCOUNTING, finer accounting of irq time -v3

On Thu, Sep 30, 2010 at 4:06 AM, Peter Zijlstra <peterz@...radead.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.

Thanks,
Venki

>
>> +       delta = now - per_cpu(irq_start_time, cpu);
>> +       per_cpu(irq_start_time, cpu) = now;
>> +       if (hardirq_count())
>> +               per_cpu(cpu_hardirq_time, cpu) += delta;
>> +       else if (in_serving_softirq())
>> +               per_cpu(cpu_softirq_time, cpu) += delta;
>> +
>> +       local_irq_restore(flags);
>> +}
>
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