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

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Date:	Mon, 24 Dec 2012 11:54:15 +0800
From:	"he, bo" <bo.he@...el.com>
To:	Randy Dunlap <rdunlap@...radead.org>
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.

Thanks randy's comments, I will modifiy it.

On Sun, 2012-12-23 at 19:37 -0800, Randy Dunlap wrote:
> 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)
> > 
> 
> 


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