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

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Date:	Sat, 7 Mar 2015 10:29:29 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	lkml <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>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 05/12] time: Add debugging checks to warn if we see delays


* John Stultz <john.stultz@...aro.org> wrote:

> Recently there's been some request for better sanity
> checking in the time code, so that its more clear
> when something is going wrong since timekeeping issues
> could manifest in a large number of strange ways with
> various subsystems.
> 
> Thus, this patch adds some extra infrastructure to
> add a check update_wall_time to print warnings if we
> see the call delayed beyond the max_cycles overflow
> point, or beyond the clocksource max_idle_ns value
> which is currently 50% of the overflow point.

Just a changelog style nit, but isn't this easier to read:

  Thus, this patch adds some extra infrastructure to
  add a check to update_wall_time() to print warnings if we
  see the call delayed beyond the 'max_cycles' overflow
  point, or beyond the clocksource 'max_idle_ns' value
  which is currently 50% of the overflow point.

?

To mark functions with parentheses and arguments in quotes, to make 
them mix better with free form English sentences?

> +#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);

s/larger then/larger than

Also, please don't break user visible messages on col80 boundaries 
just to pacify checkpatch: ignore checkpatch in these cases.

Also, plase use curly braces on multi-line statements, plus I'd shape 
it like this:

	if () {
	} else {
		if () {
		}
	}

That way the second 'if' condition in the else branch does not get 
lost in the noise of silly line breaks. (At least during email review: 
in an actual editor syntax highlighting helps.)

> +config DEBUG_TIMEKEEPING
> +	bool "Enable extra timekeeping sanity checking"
> +	help
> +	  This option will enable additional timekeeping sanity checks
> +	  which may be helpful when diagnoising issues where timekeeping

Typo.

There's really a disproportionate ratio of typos, considering how many 
iterations this patch-set has been through :-/

Or maybe I'm oversensitive to small details.

Thanks,

	Ingo
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