linux-kernel - Re: [RFC PATCH 04/16] rv/include: Add deterministic automata monitor definition via C macros

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Date:   Wed, 19 May 2021 20:27:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Kate Carcia <kcarcia@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...hat.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Gabriele Paoloni <gabriele.paoloni@...el.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>, linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH 04/16] rv/include: Add deterministic automata monitor
 definition via C macros

On Wed, May 19, 2021 at 01:36:25PM +0200, Daniel Bristot de Oliveira wrote:

> +struct da_monitor {
> +	char curr_state;
> +	bool monitoring;
> +	void *model;
> +};
> +
> +#define MAX_PID		 1024000

> +/*
> + * Functions to define, init and get a per-task monitor.
> + *
> + * XXX: Make it dynamic? make it part of the task structure?

Yes !

I'd start with maybe adding a list_head to da_monitor and embedding a
single copy into task_struct and link from there. Yes lists suck, but
how many monitors do you realistically expect to run concurrently?

> + */
> +#define DECLARE_DA_MON_INIT_PER_TASK(name, type)				\
> +										\
> +struct da_monitor da_mon_##name[MAX_PID];					\

That's ~16M of memory, which seems somewhat silly.

> +										\
> +static inline struct da_monitor *da_get_monitor_##name(pid_t pid)		\
> +{										\
> +	return &da_mon_##name[pid];						\
> +}										\
> +										\
> +void da_monitor_reset_all_##name(void)						\
> +{										\
> +	struct da_monitor *mon = da_mon_##name;					\
> +	int i;									\
> +	for (i = 0; i < MAX_PID; i++)						\
> +		da_monitor_reset_##name(&mon[i]);				\
> +}										\
> +										\
> +static void da_monitor_init_##name(void)					\
> +{										\
> +	struct da_monitor *mon = da_mon_##name;					\
> +	int i;									\
> +										\
> +	for (i = 0; i < MAX_PID; i++) {						\
> +		mon[i].curr_state = model_get_init_state_##name();		\
> +		mon[i].monitoring = 0;						\
> +		mon[i].model = model_get_model_##name();			\
> +	}									\
> +}										\