linux-kernel - Re: [PATCH 05/10] nohz: New tick dependency mask

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Date:	Mon, 3 Aug 2015 14:57:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Ingo Molnar <mingo@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 05/10] nohz: New tick dependency mask

On Thu, Jul 23, 2015 at 06:42:10PM +0200, Frederic Weisbecker wrote:
> +void tick_nohz_set_tick_dependency(enum tick_dependency_bit bit)
> +{
> +	unsigned long prev;
> +
> +	prev = __tick_nohz_set_tick_dependency(bit, &tick_dependency);
> +	if (!prev)
> +		tick_nohz_full_kick_all();
> +}

> +void tick_nohz_set_tick_dependency_cpu(enum tick_dependency_bit bit, int cpu)
> +{
> +	unsigned long prev;
> +	struct tick_sched *ts;
> +
> +	ts = per_cpu_ptr(&tick_cpu_sched, cpu);
> +
> +	prev = __tick_nohz_set_tick_dependency(bit, &ts->tick_dependency);
> +	if (!prev)
> +		tick_nohz_full_kick_cpu(cpu);
> +}

> +/*
> + * Local dependency must have its own flavour due to NMI-safe requirement
> + * on perf.
> + */

That doesn't make any sense:

  tick_nohz_set_tick_dependency_this_cpu();

(shees, you're nowhere near lazy enough, that's insane to type) is
almost identical to:

  tick_nohz_set_tick_dependency_cpu(.cpu = smp_processor_id());

The only difference is a _very_ slight reduction in cost for computing
the per-cpu offset.

> +void tick_nohz_set_tick_dependency_this_cpu(enum tick_dependency_bit bit)
> +{
> +	unsigned long prev;
> +	struct tick_sched *ts;
> +
> +	ts = this_cpu_ptr(&tick_cpu_sched);
> +
> +	prev = __tick_nohz_set_tick_dependency(bit, &ts->tick_dependency);
> +	if (!prev)
> +		tick_nohz_full_kick();
> +}


And on that naming; could we please shorten them, this is really
ridiculous, it has 'tick' in it twice.

What's wrong with:

	tick_nohz_set_dep()
	tick_nohz_set_dep_cpu()

And just kill the this_cpu() version.
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