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=-5.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 C3E62C35249 for ; Mon, 3 Feb 2020 02:04:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9045620679 for ; Mon, 3 Feb 2020 02:04:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="J/o6E/QO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727190AbgBCCEy (ORCPT ); Sun, 2 Feb 2020 21:04:54 -0500 Received: from mail-oi1-f193.google.com ([209.85.167.193]:37326 "EHLO mail-oi1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726670AbgBCCEy (ORCPT ); Sun, 2 Feb 2020 21:04:54 -0500 Received: by mail-oi1-f193.google.com with SMTP id q84so13294693oic.4; Sun, 02 Feb 2020 18:04:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=xM8qnfr4+ufIsNOSL9bq+gr1OL50xMz2+2uYLYmITCU=; b=J/o6E/QOMlK+hlpHX1+A9kZx5Mgtq0cr3vW8AiUgA7z9sUaAMOtpDa2MvqOgmcauO7 CNc5N2Q3LL34b+1MlosJPIMTMsXLc+FwsLwmXkBcfPmaHl7BY5nP9lPiIJC22qfmeAgb yftcvYePw3uYByhN3HbXFLkdz/blgGkM/l70CQwrZjNKqWNCgvxSGHN598p2FGOgfO6U 1U4le9A8KPXP/BX2AvIdD8zOm/NwE9WeylwPycrmpzat+sUxVkehSOdsjw64bSNliVKS K4PD7sngmQPd636n0RagLVB+WKXAQN4kyBmIa0ejjLPmJDv36mzOxFkRQWEONQ1KR/s7 5/HQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=xM8qnfr4+ufIsNOSL9bq+gr1OL50xMz2+2uYLYmITCU=; b=A6SmbZXQLGhX93U/p9xV+Nwzb+vSdWk0fs3TxIlobh2jH1fvcLbMfqFITY+kaOyKNT vMsaEDZ4q31MVjGYR0AsCwstHEo34iXqpKfrGQitnA5wyTdPMilFMvN74bxsb/GcdF5C mBKX/9HmIYQzbq6Ca9R4D3BZXqr3EokKHhXvJ7OL5PF6E/xO8xQHa8ynSV3w9AwdoqhF HRjxzxsfsG1HbS+LrEbNP3l42vqsF+MgNqfs7uaCDqGhTMKz7pXLTyY6Bk/8G2Wex9Tn cU1BJq9IFACEh/eYUaFjJ8DJHT7Kiy0ODwQ+QjZ/zXu0isFCDNA7+gl4XHk5gfsG+Phx hgMQ== X-Gm-Message-State: APjAAAV/+OifKJ1OmcRpezc2lD9/nBHuD2BdcJqMu8d1Jg7xvbkW/oeF Q7HRb8IS/xON/HmGzcdQIOMRv7Vb4FuwlWepbV4= X-Google-Smtp-Source: APXvYqxrf/hTN8f92ICEpDM/BV4OvPCN13XsfgERb5VDKVYxN3hJh/wlOrVvZke6AXV3cwqJLY4L7PbZyU6ejTbHVrU= X-Received: by 2002:aca:d502:: with SMTP id m2mr12724916oig.41.1580695493500; Sun, 02 Feb 2020 18:04:53 -0800 (PST) MIME-Version: 1.0 References: <20200120023326.GA149019@google.com> <8409fd7ad6b83da75c914a71accf522953a460a0.camel@pengutronix.de> In-Reply-To: From: Dave Airlie Date: Mon, 3 Feb 2020 12:04:41 +1000 Message-ID: Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification" To: Lucas Stach , Alex Deucher , Ben Skeggs , karolherbst@gmail.com Cc: "Alex G." , Bjorn Helgaas , Alexandru Gagniuc , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , David Airlie , Daniel Vetter , Jan Vesely , Lukas Wunner , Alex Williamson , Austin Bolen , Shyam Iyer , Sinan Kaya , Linux PCI , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Mon, 3 Feb 2020 at 11:56, Dave Airlie wrote: > > On Tue, 21 Jan 2020 at 21:11, Lucas Stach wrote: > > > > On Mo, 2020-01-20 at 10:01 -0600, Alex G. wrote: > > > > > > On 1/19/20 8:33 PM, Bjorn Helgaas wrote: > > > > [+cc NVMe, GPU driver folks] > > > > > > > > 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 > > > > > > > > > > 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? > > > > > > > > NVMe, GPU folks, do your drivers or devices change PCIe link > > > > speed/width for power saving or other reasons? When CONFIG_PCIE_BW=y, > > > > the PCI core interprets changes like that as problems that need to be > > > > reported. > > > > > > > > If drivers do change link speed/width, can you point me to where > > > > that's done? Would it be feasible to add some sort of PCI core > > > > interface so the driver could say "ignore" or "pay attention to" > > > > subsequent link changes? > > > > > > > > Or maybe there would even be a way to move the link change itself into > > > > the PCI core, so the core would be aware of what's going on? > > > > > > Funny thing is, I was going to suggest an in-kernel API for this. > > > * Driver requests lower link speed 'X' > > > * Link management interrupt fires > > > * If link speed is at or above 'X' then do not report it. > > > I think an "ignore" flag would defeat the purpose of having link > > > bandwidth reporting in the first place. If some drivers set it, and > > > others don't, then it would be inconsistent enough to not be useful. > > > > > > A second suggestion is, if there is a way to ratelimit these messages on > > > a per-downstream port basis. > > > > Both AMD and Nvidia GPUs have embedded controllers, which are > > responsible for the power management. IIRC those controllers can > > autonomously initiate PCIe link speed changes depending on measured bus > > load. So there is no way for the driver to signal the requested bus > > speed to the PCIe core. > > > > I guess for the GPU usecase the best we can do is to have the driver > > opt-out of the link bandwidth notifications, as the driver knows that > > there is some autonomous entity on the endpoint mucking with the link > > parameters. > > > > Adding Alex and Ben for AMD and NVIDIA info (and Karol). > > Dave.