Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752970AbbENGoS (ORCPT ); Thu, 14 May 2015 02:44:18 -0400 Received: from mail-wi0-f181.google.com ([209.85.212.181]:34739 "EHLO mail-wi0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751494AbbENGoN (ORCPT ); Thu, 14 May 2015 02:44:13 -0400 Date: Thu, 14 May 2015 08:44:07 +0200 From: Ingo Molnar To: Len Brown Cc: Jan =?iso-8859-1?Q?H=2E_Sch=F6nherr?= , Thomas Gleixner , X86 ML , "linux-kernel@vger.kernel.org" , Anthony Liguori , Ingo Molnar , "H. Peter Anvin" , Tim Deegan , Gang Wei , Linus Torvalds Subject: Re: [PATCH] x86: skip delays during SMP initialization similar to Xen Message-ID: <20150514064407.GA9117@gmail.com> References: <1430732554-7294-1-git-send-email-jschoenh@amazon.de> <20150506082759.GA30019@gmail.com> <20150507102351.GA14347@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1652 Lines: 45 * Len Brown wrote: > > [ 0.404369] x86: Booting SMP configuration: > ... > > [ 2.737884] x86: Booted up 4 nodes, 120 CPUs > > [ 2.743758] smpboot: Total of 120 processors activated (671097.18 BogoMIPS) > > > > (2.743758-0.404369) = 2.339389 for all 119 processors > > /119 = .01965873109243697478 - lets call it 19ms each > > For the record, the same (bare metal) box running latest tip boots > 10ms/processor quicker > than upstream Linux, as expected. So this 120 processor box now > boots 1.19 seconds faster, in total. > > [ 0.415969] x86: Booting SMP configuration: > ... > [ 1.553658] x86: Booted up 4 nodes, 120 CPUs > [ 1.559173] smpboot: Total of 120 processors activated (671182.14 BogoMIPS) > > 1.553658-0.415969 = 1.137689 - seconds to bring 119 processors on-line. > ./119 = .00956041176470588235 -- 9.5ms per processor, down from 19. Ok. I think we should be able to further speed that up. > 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'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? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/