Messages in this thread | | | Date | Sun, 17 May 2015 07:02:21 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: skip delays during SMP initialization similar to Xen |
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* Len Brown <lenb@kernel.org> wrote:
> On Thu, May 14, 2015 at 2:44 AM, Ingo Molnar <mingo@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
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