From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65077C10F03 for ; Tue, 23 Apr 2019 20:04:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 32D86217D9 for ; Tue, 23 Apr 2019 20:04:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="i2lc0gnE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726665AbfDWUEB (ORCPT ); Tue, 23 Apr 2019 16:04:01 -0400 Received: from mail-ed1-f67.google.com ([209.85.208.67]:43933 "EHLO mail-ed1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726043AbfDWUEA (ORCPT ); Tue, 23 Apr 2019 16:04:00 -0400 Received: by mail-ed1-f67.google.com with SMTP id j20so13798325edq.10 for ; Tue, 23 Apr 2019 13:03:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=MbOzB9oFjIbJDtZ6nzfITJuwmKLc1EH9z9Mk3KhP9Zs=; b=i2lc0gnEjEXkhGs/YcB0QHujh9D1UYVNsE4RyQDQhLFj1ye+kbGYfnsfo+g3IGgkCm rE8VcUQ962wTJq9YvGGIWmaVlq5Ei1R4VGUkTwNkVJWUlviOlNKmsKemHtgF1kmZPhiR 3pxY+gP/mgw/f3KJO2mV1GQ9RoL+ORCJ1iaGVLqqvOM9eqno3lnRKJDQ2iy5xPRPsz9L xhrUtR8KTTMzSmQlTPxbXoal6aE0Pg9GGCDFZ1ejtGLOc2y/l/mUdwxFk3u49FSdaauo UWbRwDs3dQ1pOeXuiWhOtdiR09lOeFHISyoGASv+udyv1ht8ynT3/0JYaVwSBMjvGJ8R vWYQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=MbOzB9oFjIbJDtZ6nzfITJuwmKLc1EH9z9Mk3KhP9Zs=; b=HC6NpY2JPULv9DVIMed6zrBXJrBOm3OLPV7Usmnj5AnMJvdS1lkOJTN1U9fDN/k/u3 bupvnvvyZLBHSLHoIteMch1sHn6VOmkWfvRYuPtPz/7EViP9AazOM1AHjQk8rz6u6egS 7JoCrYpjtlKEMXZppwfJ9RN/yYKEYXxD2BxxyTZ4aUUv5dysV+C2yqqmkC8hUfZWcOhy tYBx+kJZ9ysTfog3DexqAX1zIrhVxrmf+uE0TZU80UkZ0hVqQ9Hm6AzD6DoeLvpfL+7+ 0kCDkSU4XU2zhL7NkOYGRwrfckoWfO5gUwwRamgJs0OrFE0q6QWktYITL2yKnXIp5zso iqfg== X-Gm-Message-State: APjAAAXQ6DUGNWRf1iU25GB80O72hPviKYPy1kmRNewIcHLzZHJ8HWPx Qr6QnB3xda6fVbxtkWfb09Iu0LnnGEQ= X-Google-Smtp-Source: APXvYqyoBTodQDI89xOE8BCeD2YQN6spB5jF0FCzNxaPynQCQ5IYghNwbr7iTL39Nb8k+HMnYaD/TQ== X-Received: by 2002:a50:a945:: with SMTP id m5mr10694523edc.207.1556049838271; Tue, 23 Apr 2019 13:03:58 -0700 (PDT) Received: from archlinux-i9 ([2a01:4f9:2b:2b84::2]) by smtp.gmail.com with ESMTPSA id o62sm3784989eda.42.2019.04.23.13.03.57 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 23 Apr 2019 13:03:57 -0700 (PDT) Date: Tue, 23 Apr 2019 13:03:55 -0700 From: Nathan Chancellor To: Matthias Kaehlcke Cc: Sasha Levin , Greg Kroah-Hartman , stable@vger.kernel.org, Nick Desaulniers , clang-built-linux@googlegroups.com Subject: Re: Backport of commit a75bb4eb9e565b9f5115e2e8c07377ce32cbe69a Message-ID: <20190423200355.GA17824@archlinux-i9> References: <20190423190426.18720-1-natechancellor@gmail.com> <20190423193512.GP17719@sasha-vm> <20190423194512.GA31444@archlinux-i9> <20190423195628.GD112750@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190423195628.GD112750@google.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Tue, Apr 23, 2019 at 12:56:28PM -0700, Matthias Kaehlcke wrote: > On Tue, Apr 23, 2019 at 12:45:12PM -0700, Nathan Chancellor wrote: > > On Tue, Apr 23, 2019 at 03:35:12PM -0400, Sasha Levin wrote: > > > On Tue, Apr 23, 2019 at 12:04:21PM -0700, Nathan Chancellor wrote: > > > > Hi Greg and Sasha, > > > > > > > > Please apply this commit to 4.4 through 5.0 (patches are threaded in > > > > reply to this one), which will prevent Clang from emitting references > > > > to compiler runtime functions and doing some performance-killing > > > > optimization when using CONFIG_CC_OPTIMIZE_FOR_SIZE. > > > > > > > > Please let me know if I did something wrong or if there are any > > > > objections. > > > > > > This looks like a fix for a performance regression, which don't usually > > > end up in stable unless they are severe enough. > > > > > > > Yes and no. The original reason for the revert was because of the > > compiler runtime functions: > > > > https://lore.kernel.org/lkml/CAG5bF+S6OvBnsaR6UpMCqjDR9_hMo6qRMHGiW+iCaRYQW4C3YA@mail.gmail.com/ > > > > The Chromium guys hit this [1] and have applied the patch for their > > kernels, I think it should be applied for everyone. > > We picked it into our kernels because we needed a fix *now* to unbreak > our builds, but I agree it should be fixed at least in relevant LTS > versions. > Of course, I wasn't implying that was a bad thing :) it's further justification for this being a stable worthy patch as it fixes a real world issue and could fix more. > > > This patch looks simple enough, and seeing peterz on it suggests to me > > > that this was significant enough for someone to notice. Is this really > > > the case, or is this just one of those %0.01 performance regression > > > things? > > > > > > > I don't know of anyone else who has hit this but Qualcomm enabled > > CONFIG_CC_OPTIMIZE_FOR_SIZE in their 4.9 kernels with clang [2] so it > > would be nice to have this to avoid any further issues down the road. > > > > [1]: https://chromium.googlesource.com/chromiumos/third_party/kernel/+/8bb957d781e2350515c7cffd7e7dc0dfc1777f3b > > [2]: https://source.codeaurora.org/quic/la/kernel/msm-4.9/commit/?id=e828e50380a34533c37eff98345847fd74667ddd > > I suspect the Qualcomm tree would hit the VDSO issue if they use a > sufficiently recent version of clang. > > Thanks Nathan for posting this to -stable, I should have cc-ed them in > the first place. Sure thing, thanks for the reply and input! Nathan