linux-kernel - Re: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the timer

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Message-ID: <alpine.DEB.2.11.1506051140120.4155@nanos>
Date:	Fri, 5 Jun 2015 11:48:20 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	umgwanakikbuti@...il.com, mingo@...e.hu, ktkhai@...allels.com,
	rostedt@...dmis.org, juri.lelli@...il.com, pang.xunlei@...aro.org,
	oleg@...hat.com, wanpeng.li@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/14] hrtimer: Allow hrtimer::function() to free the
 timer

On Fri, 5 Jun 2015, Peter Zijlstra wrote:
>  /*
> + * We require the migration_base for lock_hrtimer_base()/switch_hrtimer_base()
> + * such that hrtimer_callback_running() can unconditionally dereference
> + * timer->base->cpu_base
> + */
> +static struct hrtimer_cpu_base migration_cpu_base = {
> +	.seq = SEQCNT_ZERO(migration_cpu_base),
> +};
> +
> +static struct hrtimer_clock_base migration_base = {
> +	.cpu_base = &migration_cpu_base,
> +};

You can spare that extra migration clock base, because
migration_cpu_base already has clock bases inside.

static struct hrtimer_cpu_base migration_cpu_base = {
	.seq = SEQCNT_ZERO(migration_cpu_base),
};

and do:

    migration_cpu_base.clock_base[CLOCK_MONOTONIC].cpu_base = &migration_cpu_base;

in hrtimer_init.

So migration base becomes: 

#define migration_base	   &migration_cpu_base.clock_base[CLOCK_MONOTONIC]

That's also more efficient in terms of cache because is two adjacent
cache lines instead of two distant ones.

Other than that, this looks good.

Thanks,

	tglx
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