linux-kernel - Re: 143e1e28 sched: Rework sched

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Message-ID: <20140720065207.GU9918@twins.programming.kicks-ass.net>
Date:	Sun, 20 Jul 2014 08:52:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Vincent Guittot <vincent.guittot@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 143e1e28 sched: Rework sched_domain topology definition

On Sun, Jul 20, 2014 at 08:43:36AM +0200, Mike Galbraith wrote:
> Hi,
> 
> +/*
> + * Topology list, bottom-up.
> + */
> +static struct sched_domain_topology_level default_topology[] = {
> +#ifdef CONFIG_SCHED_SMT
> +	{ cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT) },
> +#endif
> +#ifdef CONFIG_SCHED_MC
> +	{ cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
> +#endif
> +#ifdef CONFIG_SCHED_BOOK
> +	{ cpu_book_mask, SD_INIT_NAME(BOOK) },
> +#endif
> +	{ cpu_cpu_mask, SD_INIT_NAME(DIE) },
> +	{ NULL, },
> +};
> 
> Why did this commit rename the CPU domain to DIE?

Because they're both wrong, but we found that DIE was less wrong than
CPU.

Seeing how CPU typically means 1 logical, well, CPU, in the scheduler,
and not the package you stick on your board.

We chose DIE over PACKAGE due to 1) its shorter name and 2) things like
interlagos which have multiple DIEs in one PACKAGE etc..

Also, the only person who would ever care is the one who (with
SCHED_DEBUG) enabled looks at the topology setup, which is maybe all of
us 5.

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