linux-kernel - Re: [PATCH] printk, allow different timestamps for printk.time

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Date:	Tue, 26 Jan 2016 21:34:42 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Prarit Bhargava <prarit@...hat.com>
cc:	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
	Xunlei Pang <pang.xunlei@...aro.org>,
	Baolin Wang <baolin.wang@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Petr Mladek <pmladek@...e.cz>, Tejun Heo <tj@...nel.org>,
	Peter Hurley <peter@...leysoftware.com>,
	Vasily Averin <vvs@...tuozzo.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH] printk, allow different timestamps for printk.time

Prarit,

On Mon, 25 Jan 2016, Prarit Bhargava wrote:
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 87d40a7..2cf6692 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -3060,8 +3060,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
>  			default: disabled
>  
> -	printk.time=	Show timing data prefixed to each printk message line
> -			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
> +	printk.time=	Show timestamp prefixed to each printk message line
> +			Format: [0-2]  (0 = disable,
> +					1 = monotonic clock, 2 = real clock)

Doesn't this break systems, which have 'Y/y' on the command line?

>  static DEFINE_RAW_SPINLOCK(timekeeper_lock);
>  static struct timekeeper shadow_timekeeper;
> +static int timekeeping_active;
>  
>  /**
>   * struct tk_fast - NMI safe timekeeper
> @@ -401,6 +402,16 @@ u64 ktime_get_raw_fast_ns(void)
>  }
>  EXPORT_SYMBOL_GPL(ktime_get_raw_fast_ns);
>  
> +u64 ktime_get_log_ts(u64 *offset_real)
> +{
> +	*offset_real = ktime_to_ns(tk_core.timekeeper.offs_real);
> +
> +	if (timekeeping_active)
> +		return ktime_get_mono_fast_ns();
> +	else
> +		return local_clock();

Just for the record: The fast timekeeper stops across the inner workings of
suspend/resume. But I think that doesn't matter much.

Otherwise, this looks good now.

Thanks,

	tglx