linux-kernel - Re: [PATCH] output the cpu number when printking.

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Message-ID: <50D7CDED.4060308@infradead.org>
Date:	Sun, 23 Dec 2012 19:37:17 -0800
From:	Randy Dunlap <rdunlap@...radead.org>
To:	"he, bo" <bo.he@...el.com>
CC:	akpm@...ux-foundation.org, mingo@...e.hu, a.p.zijlstra@...llo.nl,
	linux-kernel@...r.kernel.org, yanmin_zhang@...ux.intel.com
Subject: Re: [PATCH] output the cpu number  when printking.

On 12/23/12 18:31, he, bo wrote:
> From: "he, bo" <bo.he@...el.com>
> 
> We often hit kernel panic issues on SMP machines because processes race
> on multiple cpu. By adding a new parameter printk.cpu, kernel prints
> cpu number at printk information line. It’s useful to debug what cpus
> are racing.
> 
> Signed-off-by: he, bo <bo.he@...el.com>
> ---
>  Documentation/kernel-parameters.txt |    4 ++++
>  kernel/printk.c                     |   18 ++++++++++++++++--
>  2 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index ddd84d6..ccd5266 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2378,6 +2378,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  	printk.time=	Show timing data prefixed to each printk message line
>  			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
>  
> +	printk.cpu=	Show cpu data prefixed to each printk message line
> +			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
> +	printk.cpu takes effect only when printk.time=y.

Above line needs to be indented more (beginning under "Format:").

> +
>  	processor.max_cstate=	[HW,ACPI]
>  			Limit processor to maximum C-state
>  			max_cstate=9 overrides any DMI blacklist limit.
> diff --git a/kernel/printk.c b/kernel/printk.c
> index 19c0d7b..873a226 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -863,9 +863,14 @@ static bool printk_time;
>  #endif
>  module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
>  
> +static bool printk_cpu = 1;
> +module_param_named(cpu, printk_cpu, bool, S_IRUGO | S_IWUSR);
> +
>  static size_t print_time(u64 ts, char *buf)
>  {
>  	unsigned long rem_nsec;
> +	size_t len = 0;
> +	int this_cpu;
>  
>  	if (!printk_time)
>  		return 0;
> @@ -874,8 +879,17 @@ static size_t print_time(u64 ts, char *buf)
>  		return 15;
>  
>  	rem_nsec = do_div(ts, 1000000000);
> -	return sprintf(buf, "[%5lu.%06lu] ",
> -		       (unsigned long)ts, rem_nsec / 1000);
> +
> +	if (printk_cpu) {
> +		this_cpu = raw_smp_processor_id();
> +		len = sprintf(buf, "[%5lu.%06lu,%u] ",
> +			       (unsigned long)ts, rem_nsec / 1000, this_cpu);
> +	} else {
> +		len = sprintf(buf, "[%5lu.%06lu] ",
> +			       (unsigned long)ts, rem_nsec / 1000);
> +	}
> +
> +	return len;
>  }
>  
>  static size_t print_prefix(const struct log *msg, bool syslog, char *buf)
> 


-- 
~Randy
--
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