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=-7.1 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,USER_AGENT_SANE_1 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 9A083C33CAA for ; Tue, 21 Jan 2020 14:55:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7049322314 for ; Tue, 21 Jan 2020 14:55:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="nAZN5wPU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729208AbgAUOz0 (ORCPT ); Tue, 21 Jan 2020 09:55:26 -0500 Received: from mail-ot1-f68.google.com ([209.85.210.68]:33478 "EHLO mail-ot1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727255AbgAUOz0 (ORCPT ); Tue, 21 Jan 2020 09:55:26 -0500 Received: by mail-ot1-f68.google.com with SMTP id b18so3181175otp.0; Tue, 21 Jan 2020 06:55:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=JgWyHFx4DXLB+RWjYOGV034XoPPQDPd6XzHn420fcvE=; b=nAZN5wPUP+AM+Rsbi2j/IPM4Ti4Q/3O8/f6MxlJMP3Yb02sCkRkprGqNiK0WIh/I1X Dj6ztcpmxIXxZfs+084Ps5TkXrLyDnhQZaFBs/vnssqV5cNJ3RE/bWKr6YoZvGSFat/c /4wi//wO0ZVLqCNIZ5V25i4IZzyRgdJ4sgUCqmhk7t57vd88MzlQIcy6jD9FESqIWP/v oudgj3KMqSnEpGbXGRVmTntv6Wnn2+17GBXr25HGYsRCFVpfF+r9V2iL8QOjSW3vFPcL 0liFM4dxwpkOp8jZpEL19y/d/or42DmQUtB7pa0PPIuWwM/UXrbDAI4+I2px+5jNcdW/ gvbQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=JgWyHFx4DXLB+RWjYOGV034XoPPQDPd6XzHn420fcvE=; b=Sffy+fS+S47pJzRgW6WtkG0x0fgajx7kS3Cmfe3+P/HvudweekOGTL2RoKdNa852xo npodCoCK63Aq6R+95+VlN2jLgHB5blrLrW629O/snvs7Dv1dUFAtLgR3uYm36g4DVkz9 jRVQ7iTyotHgsTRu2NnGS8qLmEsNEjDm2ezAWinjTeV9PUHljhjrX5ar/UYdrQehXumV oDr/NvthGW3hkKXqrDYmWIZzyioaI631JDDC5Vam+w4zyrDQH4O1kjQe3JEjhXWHv2mT Z7RWqfBFrKTGU1uqcgaDECMKd3MrcA0WBxaRaZsX1gbEm5GfTXHoc23Wf9jWqN+l1ExG WYbQ== X-Gm-Message-State: APjAAAXhCDm6G/zCD+DnEIC5moAXGwnI3iIYHxPlS/xFIYLoCl+WR+4n dPWOceJbp2ZApATQf24bU4O4T47JH56pww== X-Google-Smtp-Source: APXvYqyW6VsneCoGztSNubvE+lqcPqWo8gAIXD7mqMafuwj939/LThcO2TLsSXfwTjkBwSrYxC0IOA== X-Received: by 2002:a05:6830:1e11:: with SMTP id s17mr3804210otr.343.1579618524452; Tue, 21 Jan 2020 06:55:24 -0800 (PST) Received: from nuclearis2-1.gtech (c-98-195-139-126.hsd1.tx.comcast.net. [98.195.139.126]) by smtp.gmail.com with ESMTPSA id i2sm13491855oth.39.2020.01.21.06.55.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jan 2020 06:55:23 -0800 (PST) Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification" To: Lucas Stach , Bjorn Helgaas , Alexandru Gagniuc , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , David Airlie , Daniel Vetter Cc: Jan Vesely , Lukas Wunner , Alex Williamson , Austin Bolen , Shyam Iyer , Sinan Kaya , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200120023326.GA149019@google.com> <8409fd7ad6b83da75c914a71accf522953a460a0.camel@pengutronix.de> From: "Alex G." Message-ID: Date: Tue, 21 Jan 2020 08:55:22 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <8409fd7ad6b83da75c914a71accf522953a460a0.camel@pengutronix.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/21/20 5:10 AM, 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. I'm confused. Are you saying that the autonomous mechanism is causing a link bandwidth notification? Alex