From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f71.google.com (mail-lf0-f71.google.com [209.85.215.71]) by kanga.kvack.org (Postfix) with ESMTP id 5D5B96B0253 for ; Fri, 13 Oct 2017 05:03:33 -0400 (EDT) Received: by mail-lf0-f71.google.com with SMTP id f31so2021611lfi.3 for ; Fri, 13 Oct 2017 02:03:33 -0700 (PDT) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id 17sor86780ljp.68.2017.10.13.02.03.31 for (Google Transport Security); Fri, 13 Oct 2017 02:03:31 -0700 (PDT) Date: Fri, 13 Oct 2017 11:03:33 +0200 From: Johan Hovold Subject: Dramatic lockdep slowdown in 4.14 Message-ID: <20171013090333.GA17356@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Byungchul Park , Peter Zijlstra , Ingo Molnar Cc: 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 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? Johan [1] https://lkml.kernel.org/r/1502089981-21272-1-git-send-email-byungchul.park@lge.com -- 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