Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751544AbbEQFCd (ORCPT ); Sun, 17 May 2015 01:02:33 -0400 Received: from mail-wi0-f174.google.com ([209.85.212.174]:35634 "EHLO mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750787AbbEQFC0 (ORCPT ); Sun, 17 May 2015 01:02:26 -0400 Date: Sun, 17 May 2015 07:02:21 +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: <20150517050220.GA15791@gmail.com> References: <1430732554-7294-1-git-send-email-jschoenh@amazon.de> <20150506082759.GA30019@gmail.com> <20150507102351.GA14347@gmail.com> <20150514064407.GA9117@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: 1699 Lines: 51 * Len Brown wrote: > On Thu, May 14, 2015 at 2:44 AM, Ingo Molnar 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 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/