linux-kernel - Re: [PATCH 5/6] printk: Minimize time zero output

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Message-ID: <alpine.DEB.2.00.1102191733220.27722@chino.kir.corp.google.com>
Date:	Sat, 19 Feb 2011 17:51:15 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Mike Travis <travis@....com>
cc:	Ingo Molnar <mingo@...e.hu>, Jack Steiner <steiner@....com>,
	Robin Holt <holt@....com>, Len Brown <len.brown@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Yinghai Lu <yhlu.kernel@...il.com>, linux-acpi@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] printk: Minimize time zero output

On Fri, 18 Feb 2011, Mike Travis 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 |   11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> --- linux.orig/kernel/printk.c
> +++ linux/kernel/printk.c
> @@ -735,9 +735,14 @@ static inline int printk_emit_time(void)
>  	unsigned long microsec_rem;
>  
>  	t = cpu_clock(printk_cpu);
> -	microsec_rem = do_div(t, 1000000000) / 1000;
> -	tlen = sprintf(tbuf, "[%5lu.%06lu] ", (unsigned long)t, microsec_rem);
> -
> +	if (likely(t)) {
> +		microsec_rem = do_div(t, 1000000000) / 1000;
> +		tlen = sprintf(tbuf, "[%5lu.%06lu] ",
> +					(unsigned long)t, microsec_rem);

The definition of microsec_rem can become local to this clause.

> +	} else {
> +		/* reduce byte count in log when time is zero */
> +		tlen = sprintf(tbuf, "[0] ");

If we know the padding when cpu_clock() is non-zero, then why not make 
sure the kernel log is aligned properly by using the same padding here?

> +	}
>  	for (tp = tbuf; tp < tbuf + tlen; tp++)
>  		emit_log_char(*tp);
>  
--
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