linux-kernel - Re: [PATCH 6/7] psi: pressure stall information for CPU, memory, and IO

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Date:   Wed, 9 May 2018 11:59:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-block@...r.kernel.org, cgroups@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Mike Galbraith <efault@....de>,
        Oliver Yang <yangoliver@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        xxx xxx <x.qendo@...il.com>,
        Taras Kondratiuk <takondra@...co.com>,
        Daniel Walker <danielwa@...co.com>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Ruslan Ruslichenko <rruslich@...co.com>, kernel-team@...com
Subject: Re: [PATCH 6/7] psi: pressure stall information for CPU, memory, and
 IO

On Mon, May 07, 2018 at 05:01:34PM -0400, Johannes Weiner wrote:
> diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
> new file mode 100644
> index 000000000000..b22b0ffc729d
> --- /dev/null
> +++ b/include/linux/psi_types.h
> @@ -0,0 +1,84 @@
> +#ifndef _LINUX_PSI_TYPES_H
> +#define _LINUX_PSI_TYPES_H
> +
> +#include <linux/types.h>
> +
> +#ifdef CONFIG_PSI
> +
> +/* Tracked task states */
> +enum psi_task_count {
> +	NR_RUNNING,
> +	NR_IOWAIT,
> +	NR_MEMSTALL,
> +	NR_PSI_TASK_COUNTS,
> +};
> +
> +/* Task state bitmasks */
> +#define TSK_RUNNING	(1 << NR_RUNNING)
> +#define TSK_IOWAIT	(1 << NR_IOWAIT)
> +#define TSK_MEMSTALL	(1 << NR_MEMSTALL)
> +
> +/* Resources that workloads could be stalled on */
> +enum psi_res {
> +	PSI_CPU,
> +	PSI_MEM,
> +	PSI_IO,
> +	NR_PSI_RESOURCES,
> +};
> +
> +/* Pressure states for a group of tasks */
> +enum psi_state {
> +	PSI_NONE,		/* No stalled tasks */
> +	PSI_SOME,		/* Stalled tasks & working tasks */
> +	PSI_FULL,		/* Stalled tasks & no working tasks */
> +	NR_PSI_STATES,
> +};
> +
> +struct psi_resource {
> +	/* Current pressure state for this resource */
> +	enum psi_state state;
> +
> +	/* Start of current state (cpu_clock) */
> +	u64 state_start;
> +
> +	/* Time sampling buckets for pressure states (ns) */
> +	u64 times[NR_PSI_STATES - 1];

Fails to explain why no FULL.

> +};
> +
> +struct psi_group_cpu {
> +	/* States of the tasks belonging to this group */
> +	unsigned int tasks[NR_PSI_TASK_COUNTS];
> +

AFAICT there's a hole here, that would fit the @nonidle member. Which
also avoids the later hole generated by it.

> +	/* Per-resource pressure tracking in this group */
> +	struct psi_resource res[NR_PSI_RESOURCES];
> +
> +	/* There are runnable or D-state tasks */
> +	bool nonidle;

Mandatory complaint about using _Bool in composites goes here.

> +	/* Start of current non-idle state (cpu_clock) */
> +	u64 nonidle_start;
> +
> +	/* Time sampling bucket for non-idle state (ns) */
> +	u64 nonidle_time;
> +};
> +
> +struct psi_group {
> +	struct psi_group_cpu *cpus;
> +
> +	struct delayed_work clock_work;
> +	unsigned long period_expires;
> +
> +	u64 some[NR_PSI_RESOURCES];
> +	u64 full[NR_PSI_RESOURCES];
> +
> +	unsigned long avg_some[NR_PSI_RESOURCES][3];
> +	unsigned long avg_full[NR_PSI_RESOURCES][3];
> +};