linux-kernel - Re: [PATCH 4/5] printk: Minimize time zero output

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Date:	Fri, 18 Feb 2011 08:34:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Mike Travis <travis@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <len.brown@...el.com>,
	Yinghai Lu <yhlu.kernel@...il.com>, linux-acpi@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] printk: Minimize time zero output


* Mike Travis <travis@....com> wrote:

> Reduce the length for time zero messages by only printing "[0] ".
> 
> v2: updated to apply to x86-tip
> 
> Signed-off-by: Mike Travis <travis@....com>
> Reviewed-by: Jack Steiner <steiner@....com>
> Reviewed-by: Robin Holt <holt@....com>
> ---
>  kernel/printk.c |    8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> --- linux.orig/kernel/printk.c
> +++ linux/kernel/printk.c
> @@ -818,11 +818,13 @@ asmlinkage int vprintk(const char *fmt,
>  				unsigned long nanosec_rem;
>  
>  				t = cpu_clock(printk_cpu);
> -				nanosec_rem = do_div(t, 1000000000);
> -				tlen = sprintf(tbuf, "[%5lu.%06lu] ",
> +				if (likely(t)) {
> +					nanosec_rem = do_div(t, 1000000000);
> +					tlen = sprintf(tbuf, "[%5lu.%06lu] ",
>  						(unsigned long) t,
>  						nanosec_rem / 1000);

The excessive number of very ugly linebreaks in this statement should have told you 
that the whole printk_time function wants to be broken out of vsprintk(), into a 
helper function.

Please make it two patches: one cleanup-only patch that factors out the code, the 
second one that modifies it materially.

Thanks,

	Ingo
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