linux-kernel - Re: [PATCH 4/5] irqtime: Move irqtime entry accounting after irq offset incrementation

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Message-ID: <87im9lhibd.fsf@nanos.tec.linutronix.de>
Date:   Tue, 01 Dec 2020 12:33:26 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Tony Luck <tony.luck@...el.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Heiko Carstens <hca@...ux.ibm.com>
Subject: Re: [PATCH 4/5] irqtime: Move irqtime entry accounting after irq offset incrementation

On Tue, Dec 01 2020 at 10:20, Peter Zijlstra wrote:
> On Tue, Dec 01, 2020 at 01:12:25AM +0100, Frederic Weisbecker wrote:
> Why not something like:
>
> void irqtime_account_irq(struct task_struct *curr, unsigned int offset)
> {
> 	struct irqtime *irqtime = this_cpu_ptr(&cpu_irqtime);
> 	unsigned int pc = preempt_count() - offset;
> 	s64 delta;
> 	int cpu;
>
> 	if (!sched_clock_irqtime)
> 		return;
>
> 	cpu = smp_processor_id();
> 	delta = sched_clock_cpu(cpu) - irqtime->irq_start_time;
> 	irqtime->irq_start_time += delta;
>
> 	/*
> 	 * We do not account for softirq time from ksoftirqd here.
> 	 * We want to continue accounting softirq time to ksoftirqd thread
> 	 * in that case, so as not to confuse scheduler with a special task
> 	 * that do not consume any time, but still wants to run.
> 	 */
> 	if (pc & HARDIRQ_MASK)
> 		irqtime_account_delta(irqtime, delta, CPUTIME_IRQ);
> 	else if ((pc & SOFTIRQ_OFFSET) && curr != this_cpu_ksoftirqd())
> 		irqtime_account_delta(irqtime, delta, CPUTIME_SOFTIRQ);
> }

Why not making all of this explicit instead of these conditionals?

Thanks,

        tglx