From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id BC67A6B0033 for ; Fri, 13 Oct 2017 05:07:52 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id n14so7656448pfh.15 for ; Fri, 13 Oct 2017 02:07:52 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [65.50.211.133]) by mx.google.com with ESMTPS id f3si353523plb.556.2017.10.13.02.07.50 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 13 Oct 2017 02:07:50 -0700 (PDT) Date: Fri, 13 Oct 2017 11:07:44 +0200 From: Peter Zijlstra Subject: Re: Dramatic lockdep slowdown in 4.14 Message-ID: <20171013090744.lvvc66qexmomsd5f@hirez.programming.kicks-ass.net> References: <20171013090333.GA17356@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171013090333.GA17356@localhost> Sender: owner-linux-mm@kvack.org List-ID: To: Johan Hovold Cc: Byungchul Park , Ingo Molnar , linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-mm@kvack.org, kernel-team@lge.com, Tony Lindgren , Arnd Bergmann , linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org On Fri, Oct 13, 2017 at 11:03:33AM +0200, Johan Hovold wrote: > Hi, > > I had noticed that the BeagleBone Black boot time appeared to have > increased significantly with 4.14 and yesterday I finally had time to > investigate it. > > Boot time (from "Linux version" to login prompt) had in fact doubled > since 4.13 where it took 17 seconds (with my current config) compared to > the 35 seconds I now see with 4.14-rc4. > > I quick bisect pointed to lockdep and specifically the following commit: > > 28a903f63ec0 ("locking/lockdep: Handle non(or multi)-acquisition > of a crosslock") > > which I've verified is the commit which doubled the boot time (compared > to 28a903f63ec0^) (added by lockdep crossrelease series [1]). > > I also verified that simply disabling CONFIG_PROVE_LOCKING on 4.14-rc4 > brought boot time down to about 14 seconds. > > Now since it's lockdep I guess this can't really be considered a > regression if these changes did improve lockdep correctness, but still, > this dramatic slow down essentially forces me to disable PROVE_LOCKING > by default on this system. > > Is this lockdep slowdown expected and desirable? Expected yes, desirable not so much. Its the save_stack_trace() in add_xhlock() (IIRC). I've not yet had time to figure out what to do about that. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org