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=-11.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 368A6C433E6 for ; Thu, 28 Jan 2021 23:40:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E950664DE2 for ; Thu, 28 Jan 2021 23:40:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231237AbhA1XkP (ORCPT ); Thu, 28 Jan 2021 18:40:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:52662 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229828AbhA1XkM (ORCPT ); Thu, 28 Jan 2021 18:40:12 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id E778364DE2; Thu, 28 Jan 2021 23:39:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611877171; bh=uCYlOxWFyGqfzsCOjgAMNaqNNqAKRulWHpgwkwEgtJ0=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=RQNMLRsXqregPQH2liQAw5L0gRasHqMLwn0Bz9kiNzAqOK0GMBn/pUCkD/S/iIv5k rltYgHbPb8y4r+8on6aa+T8GqVHL2CsYQhzzyenOwKqfLbof30U6FheCKJgyZW46Fc D+s1Xb+qcCbjYSNQ7XrcRKZCEvrbsNBdkT2Y6RRUxtqT6t1DKJmWXtRFy7oC1WSozc zd23P1uiAF9dkA8yQQAaTswCZ/Fo+U6IFokq7IxTQWf8GyFDTuEGMf9kf7LyZmWj+R as+D/W8BBFiCROZtd+kN9ZQH/yGtBf5ysvyHYPLjgDgu4AD8EXmgbKlIsp8cRkfZ1I bAL/Czktx315A== Date: Thu, 28 Jan 2021 17:39:29 -0600 From: Bjorn Helgaas To: Alexandru Gagniuc , Alexandru Gagniuc , Keith Busch Cc: Jan Vesely , Lukas Wunner , Alex Williamson , Austin Bolen , Shyam Iyer , Sinan Kaya , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Lucas Stach , Dave Airlie , Ben Skeggs , Alex Deucher , Myron Stowe , "A. Vladimirov" Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification" Message-ID: <20210128233929.GA39660@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200222165840.GA214760@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org [+cc Atanas -- thank you very much for the bug report!] On Sat, Feb 22, 2020 at 10:58:40AM -0600, Bjorn Helgaas wrote: > On Wed, Jan 15, 2020 at 04:10:08PM -0600, Bjorn Helgaas wrote: > > I think we have a problem with link bandwidth change notifications > > (see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/pcie/bw_notification.c). > > > > Here's a recent bug report where Jan reported "_tons_" of these > > notifications on an nvme device: > > https://bugzilla.kernel.org/show_bug.cgi?id=206197 > > AFAICT, this thread petered out with no resolution. > > If the bandwidth change notifications are important to somebody, > please speak up, preferably with a patch that makes the notifications > disabled by default and adds a parameter to enable them (or some other > strategy that makes sense). > > I think these are potentially useful, so I don't really want to just > revert them, but if nobody thinks these are important enough to fix, > that's a possibility. Atanas is also seeing this problem and went to the trouble of digging up this bug report: https://bugzilla.kernel.org/show_bug.cgi?id=206197#c8 I'm actually a little surprised that we haven't seen more reports of this. I don't think distros enable CONFIG_PCIE_BW, but even so, I would think more people running upstream kernels would trip over it. But maybe people just haven't turned CONFIG_PCIE_BW on. I don't have a suggestion; just adding Atanas to this old thread. > > There was similar discussion involving GPU drivers at > > https://lore.kernel.org/r/20190429185611.121751-2-helgaas@kernel.org > > > > The current solution is the CONFIG_PCIE_BW config option, which > > disables the messages completely. That option defaults to "off" (no > > messages), but even so, I think it's a little problematic. > > > > Users are not really in a position to figure out whether it's safe to > > enable. All they can do is experiment and see whether it works with > > their current mix of devices and drivers. > > > > I don't think it's currently useful for distros because it's a > > compile-time switch, and distros cannot predict what system configs > > will be used, so I don't think they can enable it. > > > > Does anybody have proposals for making it smarter about distinguishing > > real problems from intentional power management, or maybe interfaces > > drivers could use to tell us when we should ignore bandwidth changes? > > > > Bjorn