linux-kernel - Re: [RFC PATCH v3 11/16] sched: Basic tracking of matching tasks

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Date:   Mon, 26 Aug 2019 13:59:03 -0700
From:   mark gross <mgross@...ux.intel.com>
To:     Vineeth Remanan Pillai <vpillai@...italocean.com>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>, mingo@...nel.org,
        tglx@...utronix.de, pjt@...gle.com, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, subhra.mazumdar@...cle.com,
        fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
        Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v3 11/16] sched: Basic tracking of matching tasks

On Wed, May 29, 2019 at 08:36:47PM +0000, Vineeth Remanan Pillai wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> Introduce task_struct::core_cookie as an opaque identifier for core
> scheduling. When enabled; core scheduling will only allow matching
> task to be on the core; where idle matches everything.
> 
> When task_struct::core_cookie is set (and core scheduling is enabled)
> these tasks are indexed in a second RB-tree, first on cookie value
> then on scheduling function, such that matching task selection always
> finds the most elegible match.
> 
> NOTE: *shudder* at the overhead...
> 
> NOTE: *sigh*, a 3rd copy of the scheduling function; the alternative
> is per class tracking of cookies and that just duplicates a lot of
> stuff for no raisin (the 2nd copy lives in the rt-mutex PI code).
 s/raisen/reason

> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Vineeth Remanan Pillai <vpillai@...italocean.com>
> Signed-off-by: Julien Desfossez <jdesfossez@...italocean.com>
> ---
> 
> Changes in v3
> -------------
> - Refactored priority comparison code
> - Fixed a comparison logic issue in sched_core_find
>   - Aaron Lu
> 
> Changes in v2
> -------------
> - Improves the priority comparison logic between processes in
>   different cpus.
>   - Peter Zijlstra
>   - Aaron Lu
> 
> ---
>  include/linux/sched.h |   8 ++-
>  kernel/sched/core.c   | 146 ++++++++++++++++++++++++++++++++++++++++++
>  kernel/sched/fair.c   |  46 -------------
>  kernel/sched/sched.h  |  55 ++++++++++++++++
>  4 files changed, 208 insertions(+), 47 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 1549584a1538..a4b39a28236f 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -636,10 +636,16 @@ struct task_struct {
>  	const struct sched_class	*sched_class;
>  	struct sched_entity		se;
>  	struct sched_rt_entity		rt;
> +	struct sched_dl_entity		dl;
> +
> +#ifdef CONFIG_SCHED_CORE
> +	struct rb_node			core_node;
> +	unsigned long			core_cookie;
> +#endif
> +
>  #ifdef CONFIG_CGROUP_SCHED
>  	struct task_group		*sched_task_group;
>  #endif
> -	struct sched_dl_entity		dl;
>  
>  #ifdef CONFIG_PREEMPT_NOTIFIERS
>  	/* List of struct preempt_notifier: */
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b1ce33f9b106..112d70f2b1e5 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -64,6 +64,141 @@ int sysctl_sched_rt_runtime = 950000;
>  
>  DEFINE_STATIC_KEY_FALSE(__sched_core_enabled);
>  
> +/* kernel prio, less is more */
> +static inline int __task_prio(struct task_struct *p)
> +{
> +	if (p->sched_class == &stop_sched_class) /* trumps deadline */
> +		return -2;
> +
> +	if (rt_prio(p->prio)) /* includes deadline */
> +		return p->prio; /* [-1, 99] */
> +
> +	if (p->sched_class == &idle_sched_class)
> +		return MAX_RT_PRIO + NICE_WIDTH; /* 140 */
> +
> +	return MAX_RT_PRIO + MAX_NICE; /* 120, squash fair */
> +}
> +
> +/*
> + * l(a,b)
> + * le(a,b) := !l(b,a)
> + * g(a,b)  := l(b,a)
> + * ge(a,b) := !l(a,b)
why does this truth table comment exist?
maybe inline comments at the confusing inequalities would be better.
--mark