Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1034082AbcJRRTs (ORCPT ); Tue, 18 Oct 2016 13:19:48 -0400 Received: from mail-oi0-f67.google.com ([209.85.218.67]:35844 "EHLO mail-oi0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S939012AbcJRRTb (ORCPT ); Tue, 18 Oct 2016 13:19:31 -0400 MIME-Version: 1.0 In-Reply-To: References: From: Linus Torvalds Date: Tue, 18 Oct 2016 10:19:25 -0700 X-Google-Sender-Auth: l0r8MoH0LVxHKAm3Gfvy3-QSiK8 Message-ID: Subject: Re: [4.9-rc1] Build-time 2x slower To: =?UTF-8?Q?J=C3=B6rg_Otte?= , Michal Marek Cc: Sedat Dilek , Ming Lei , LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id u9IHJvdM012403 Content-Length: 1899 Lines: 56 On Tue, Oct 18, 2016 at 9:49 AM, Jörg Otte wrote: > On Tue, Oct 18, 2016 at 12:04 AM, Sedat Dilek wrote: >> >> not sure whom to address on this issue. >> >> I have built Linux v4.9-rc1, v4.8.2 and v4.4.25 kernels (in this >> order) this morning. >> >> Building a Linux v4.8.2 under Linux v4.9-rc1 took two times longer. >> >> As usually I build with 2 parallel-make-jobs. >> This takes approx. 30mins. >> Under Linux v4.9-rc1 it took approx. an hour. >> >> My system is a Ubuntu/precise AMD64 (WUBI installation). >> I use my normal build-environment. > > I can confirm the problem. I use 3 build jobs in parallel > and the kernel build takes 2,5 times longer. > > I'm only seeing 1 (of 4) cores are running with max frequency. > The other are running in minimum frequency. And this seems not > to be limited to build jobs however. > > The last known good kernel for me is ..-4.8.0-14604-g29fbff8 Well, there are a few merges in 4.9-rc1 since that 4.8.0-14604-g29fbff8 version, but the obvious ones are my pulls from: Michal Marek (2): kbuild updates misc kbuild changes (My merge commit ID's are 50cff89837a4 and 84d69848c97f) with everything else looking like "normal code updates". Michal: a 2.5x slowdown of the kernel build was presumably *not* intentional. I'm not seeing anything obvious, but if it's spending a lot more time in fixdep, then it's that "strstr()" change. That commit seems to assume that strstr() is fast, which is a debatable assumption and might be wrong in some environments. But even with a "strstr()" written by a sloth that was dropped on its head a few too many times when young, I can't see it being *that* much slower. Can you do just a silly perf record make -j8 of the bad build, and see if something stands out when you do "perf report"? But maybe Michal has some ideas. Linus