* Len Brown <l...@kernel.org> wrote:
> On Thu, May 14, 2015 at 2:44 AM, Ingo Molnar <mi...@kernel.org> wrote:
>
> >
> >> BTW. this time can be reduced by 7% (113 ms) by deleting
> >> announce_cpu():
> >>
> >> [ 1.445815] x86: Booted up 4 nodes, 120 CPUs
> >
> > so that kind of info looks pretty useful, especially when there's
> > hangs/failures.
>
> I think the messages we print on failure are useful.
> I think the success case should be a 1-line summary.
But we usually don't know a failure until it happens, and then people
often don't know which quirky debug option to turn on before sending a
capture of the failure.
It also pretty compressed and looks kind of cool, especially with
larger CPU counts. Would love to see a 6K CPUs system boot up ;-)
> > I'm wondering what takes 113 msecs to print 120 CPUs - that's
> > about 1 msec per a few chars of printk produced, seems excessive.
> > Do you have any idea what's going on there? Does your system print
> > to a serial console perhaps?
>
> Yes, serial console -- that server is actually much
> closer to you than it is to me, it is in Finland:-)
LOL ;-)
> I should benchmark it, because 115200 should be faster...
So 115200 baud == 14400 bytes/sec == 14.4 bytes/msec == 0.07 msecs/byte
So with 120 CPUs we print about 5-6 chars per CPU, which is 6*120==720
bytes, which should take about 50 msecs.
So serial explains about half of the observed overhead.
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
