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=-7.7 required=3.0 tests=BAYES_00,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=no 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 5D7D6C433DB for ; Fri, 29 Jan 2021 01:32:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 28F7164DF1 for ; Fri, 29 Jan 2021 01:32:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231663AbhA2Bbl (ORCPT ); Thu, 28 Jan 2021 20:31:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44060 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231421AbhA2BbX (ORCPT ); Thu, 28 Jan 2021 20:31:23 -0500 Received: from mail-ot1-x32a.google.com (mail-ot1-x32a.google.com [IPv6:2607:f8b0:4864:20::32a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 91146C061574; Thu, 28 Jan 2021 17:30:42 -0800 (PST) Received: by mail-ot1-x32a.google.com with SMTP id k8so7177446otr.8; Thu, 28 Jan 2021 17:30:42 -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=cGKWZfOvrSWPATU3fA4o+Sejn9j2AxeGUg6tCFIll98=; b=jkvuUnBsIg+7yormfly8fvT/Y+lJzqwcBvLDM0c4Dlb08Cgn/a+t5M+0++Gp4COXS1 fElA6rU3UdMVfSHmcAX/VAlM91kz8UbvQSV/U4VwReSs+jeO8amA9aaG4ZpFkQVCekr7 OmgzYpXxEKQVvHwwKdgPZ4s0BWhC4EMG3dwisY8IuDra6n9DRzd3B/mxMUApTZg2CQVZ jZMdUUwFFUi7Y3jT7MEEljzd83YeX7ar7h+eFMdMbiDzFn5wwrH9wReTOJREByRyATQB MHSvqxgHF+xomJaKIeTZ7Cdxh+qIPpXUmHXla8qJZh4rl7+Fgg5TFZMVpuqtxiJjto+M sVIA== 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=cGKWZfOvrSWPATU3fA4o+Sejn9j2AxeGUg6tCFIll98=; b=s/BalyTKnv0W65WH93EsDfJMEkM5YetoeLgFqBVotaTGK7YuTo1AJ1YXsUWct3MGpy R0zIZC+VazJUWhscF9w6gyH70//sdekrA+b8KGZDNX5pbS9h2cTM0sZZGkUeOBI2uoW1 qM9Q5h3gr9XV4u1qJcSK8WyU82bhdyMWUEf35ZjWjCBFrS6EQK6IPL6yG+OTeslxd6Fr 8WaJ3BPkgJ8ZpX7WmR/GVdgbWTdBqo/Mln4zzOWSOde9+7EsydMtjA0tJNwb5uQrLQ9H 8DpbrPpWydxkkruABFvozCv1R43QtD4W+nyXC/g8rxvobVGVqy9OpA+2s7cCxnyKON/c 66cA== X-Gm-Message-State: AOAM533bkJMwozHKXjpF2ejXcr8OcdvZsV9N+rEVU48YksIaEGAUcmNp +yp0KH31kz7PG3yrIeZuaU2BpYKeg0uL//N6pNM= X-Google-Smtp-Source: ABdhPJxahw8SU4xkm8h1Lu4hXo7R8sh8LWlxy9e/S++UZwV8fzg0GTI/oiMiXsgg3YT4Kc7g/8+ryyV++gPb+LxO37s= X-Received: by 2002:a9d:1293:: with SMTP id g19mr1487102otg.311.1611883841513; Thu, 28 Jan 2021 17:30:41 -0800 (PST) MIME-Version: 1.0 References: <20200222165840.GA214760@google.com> <20210128233929.GA39660@bjorn-Precision-5520> In-Reply-To: <20210128233929.GA39660@bjorn-Precision-5520> From: Alex Deucher Date: Thu, 28 Jan 2021 20:30:30 -0500 Message-ID: Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification" To: Bjorn Helgaas Cc: Alexandru Gagniuc , Alexandru Gagniuc , Keith Busch , Jan Vesely , Lukas Wunner , Alex Williamson , Austin Bolen , Shyam Iyer , Sinan Kaya , Linux PCI , LKML , Christoph Hellwig , Lucas Stach , Dave Airlie , Ben Skeggs , Myron Stowe , "A. Vladimirov" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, Jan 28, 2021 at 6:39 PM Bjorn Helgaas wrote: > > [+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? There's also this recently filed bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1447 The root cause of it appears to be related to ASPM. Alex