linux-kernel - Re: [PATCH V3] sched/isolation: isolate from handling managed interrupt

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Date:   Mon, 20 Jan 2020 16:58:49 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Peter Xu <peterx@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH V3] sched/isolation: isolate from handling managed
 interrupt

Hello Thomas,

On Sun, Jan 19, 2020 at 05:50:17PM +0100, Thomas Gleixner wrote:
> Ming,
> 
> Ming Lei <ming.lei@...hat.com> writes:
> >  
> > +static bool hk_should_isolate(struct irq_data *data,
> > +		const struct cpumask *affinity, unsigned int cpu)
> 
> Please align the first argument on the second line with the first
> argument on the first line.
> 
> > +{
> > +	const struct cpumask *hk_mask;
> > +
> > +	if (!housekeeping_enabled(HK_FLAG_MANAGED_IRQ))
> > +		return false;
> > +
> > +	if (!irqd_affinity_is_managed(data))
> > +		return false;
> 
> Pointless. That's already checked at the begin of the calling function.
> 
> > +
> > +	if (!cpumask_test_cpu(cpu, affinity))
> > +		return false;
> 
> Ditto.
> 
> > +	hk_mask = housekeeping_cpumask(HK_FLAG_MANAGED_IRQ);
> > +	if (cpumask_subset(affinity, hk_mask))
> > +		return false;
> > +
> > +	if (cpumask_intersects(irq_data_get_effective_affinity_mask(data),
> > +				hk_mask))
> 
> I really had to think twice why this is correct. The example I gave you
> is far more intuitive. It's just missing the check below.

Your example uses isolation mask, which has to be allocated and built
from housekeeping_cpumask(HK_FLAG_MANAGED_IRQ), that is why I use the
above way so that we can avoid the allocation.

IMO, the above is intuitive too, given it can be thought as effective
affinity including hk CPUs.

Thanks,
Ming