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

David Rientjes
2014-04-24T22:19:00Z

On Fri, 25 Apr 2014, Jiri Kosina 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?
>

I think he's referring to the alignment with %02x.

> > 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.
>

Sounds like the appropriate fix would be to serialize stack dumping to the
kernel log.