linux-kernel - Re: [PATCH v2] sched: Enabled schedstat when schedstat tracepoints are enabled

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Message-Id: <20170413110548.GL6820@linux.vnet.ibm.com>
Date:   Thu, 13 Apr 2017 04:05:48 -0700
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Mel Gorman <mgorman@...e.de>, LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH v2] sched: Enabled schedstat when schedstat tracepoints
 are enabled

> +#if defined(CONFIG_TRACING) && defined(CONFIG_SCHEDSTATS)
> +int schedstat_tracepoint_reg(void);
> +void schedstat_tracepoint_unreg(void);
> +#else
> +static inline int schedstat_tracepoint_reg(void) { return 0; }
> +static inline void schedstat_tracepoint_unreg(void) { }
> +#endif
> +
> 


> +#ifdef CONFIG_TRACING

Shouldn't this be also
> +#if defined(CONFIG_TRACING) && defined(CONFIG_SCHEDSTATS) ????

If CONFIG_TRACING is defined but CONFIG_SCHEDSTATS is not then build
should complain about duplicate schedstat_tracepoint_reg(). No?

> +static int schedstat_tracepoint_ref;
> +static bool schedstat_save_state;
> +/*
> + * schedstat_tracepoint_reg() and unreg() are called by the tracepoint
> + * regfunc/unregfunc functions. They are protected by the tracepoint mutex.
> + *     See kernel/tracepoint.c:tracepoint_add_func().
> + *
> + * The modifications to schedstat_tracepoint_ref and schedstat_save_state
> + * are only done under that mutex, and do not need further protection.
> + */
> +int schedstat_tracepoint_reg(void)
> +{
> +	if (!schedstat_tracepoint_ref) {
> +		schedstat_save_state = schedstat_enabled();
> +		if (!schedstat_save_state)
> +			set_schedstats(true);
> +	}
> +	schedstat_tracepoint_ref++;
> +	return 0;
> +}
> +
> +void schedstat_tracepoint_unreg(void)
> +{
> +	schedstat_tracepoint_ref--;
> +	if (schedstat_tracepoint_ref || schedstat_save_state)
> +		return;
> +	set_schedstats(false);
> +}
> +#endif