Re: [PATCH] printk: Print cpu number along with time

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Apr 25, 2014 at 12:12:06AM +0200, Jiri Kosina wrote:
> On Thu, 24 Apr 2014, Greg Kroah-Hartman wrote:
> 
> > > +#ifdef CONFIG_PRINTK_CPU
> > > +	if (!buf)
> > > +		return snprintf(NULL, 0, "[%5lu.000000,%02x] ",
> > 
> > %02x for a cpu?  What happens on machines with 8k cpus?
> 
> Ummm ... what issue do you see here, Greg? It'll print 0x1f40, no?

Yes, just not be as "pretty" and aligned properly :)

> > And is this really an issue?  Debugging by using printk is fun, but not 
> > really something that people need to add a cpu number to.  Why not just 
> > use a tracepoint in your code to get the needed information instead?
> 
> Well, if you have dmesg dump from panic that happens every other year, and 
> you have to do post-mortem analysis on it, I am pretty sure you would love 
> to be able to figure out how the stack traces would look like without 
> inter-CPU interleaving. And I am pretty sure you wouldn't want to 
> insert/enable a tracepoint and wait another two years for the bug to 
> trigger again.

Fair enough, and the multi-oops message drives that home.

But does this break things like 'dmesg --human' mode that is in
util-linux?

thanks,

greg k-h