linux-kernel - Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM

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Date:	Fri, 10 Dec 2010 18:18:20 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Mikael Pettersson <mikpe@...uu.se>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	John Stultz <johnstul@...ibm.com>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [BUG] 2.6.37-rc3 massive interactivity regression on ARM

Le vendredi 10 décembre 2010 à 14:47 +0100, Peter Zijlstra a écrit :
> Full patch..

> unt_system_vtime(struct task_struct *curr)
>  {
>  	unsigned long flags;
> +	s64 delta;
>  	int cpu;
> -	u64 now, delta;
>  
>  	if (!sched_clock_irqtime)
>  		return;
>  
>  	local_irq_save(flags);
> -
>  	cpu = smp_processor_id();
> -	now = sched_clock_cpu(cpu);
> -	delta = now - per_cpu(irq_start_time, cpu);
> -	per_cpu(irq_start_time, cpu) = now;
> -	/*
> -	 * 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.
> -	 */
> +	delta = sched_clock_cpu(cpu) - per_cpu(irq_start_time, cpu);
> +	per_cpu(irq_start_time, cpu) += delta;

We should add some checkpatch warning to any new per_cpu() use.


	delta = sched_clock_cpu(cpu) - __this_cpu_read(irq_start_time);
	__this_cpu_add(irq_start_time, delta);



Also irq_time_write_begin() and irq_time_write_end() could be faster
(called for current cpu)

static inline void irq_time_write_begin(void)
{
	__this_cpu_inc(irq_time_seq.sequence);
	smp_wmb();
}
 
static inline void irq_time_write_end(void)
{
	smp_wmb();
	__this_cpu_inc(irq_time_seq.sequence);
}
 


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