linux-kernel - Re: [PATCH] x86: skip delays during SMP initialization similar to Xen

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Date:	Sat, 16 May 2015 04:46:17 -0400
From:	Len Brown <lenb@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Jan H. Schönherr <jschoenh@...zon.de>,
	Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Anthony Liguori <aliguori@...zon.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Tim Deegan <tim@....org>,
	Gang Wei <gang.wei@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: skip delays during SMP initialization similar to Xen

On Thu, May 14, 2015 at 2:44 AM, Ingo Molnar <mingo@...nel.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.

> 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:-)

I should benchmark it, because 115200 should be faster...

cheers,
Len Brown, Intel Open Source Technology Center
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