linux-kernel - Re: [PATCH 05/12] time: Add debugging checks to warn if we see delays

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Message-ID: <20150123142702.GA23123@twins.programming.kicks-ass.net>
Date:	Fri, 23 Jan 2015 15:27:02 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...emonkey.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Cochran <richardcochran@...il.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 05/12] time: Add debugging checks to warn if we see delays

On Thu, Jan 22, 2015 at 04:09:20PM -0800, John Stultz wrote:
> +#ifdef CONFIG_DEBUG_TIMEKEEPING
> +static void timekeeping_check_update(struct timekeeper *tk, cycle_t offset)
> +{
> +
> +	cycle_t max_cycles = tk->tkr.clock->max_cycles;
> +	const char *name = tk->tkr.clock->name;
> +
> +	if (offset > max_cycles)
> +		printk_deferred("ERROR: cycle offset (%lld) is larger then"
> +			" allowed %s max_cycles (%lld)\n",
> +			offset, name, max_cycles);
> +	else if (offset > (max_cycles >> 1))
> +		printk_deferred("WARNING: cycle offset (%lld) is past"
> +			" the %s 50%% safety margin (%lld)\n",
> +			offset, name, max_cycles>>1);
> +}
> +#else
> +#define timekeeping_check_update(x, y)

static inline void timekeeping_check_update(struct timekeeper *tk, cycle_t offset) { }

Would preserve argument type checks. The only argument for using a macro
here would be to avoid evaluating the arguments, but that's not an issue
in this case afaict.

> +#endif
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