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=-7.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FAKE_REPLY_C,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 47C51C35671 for ; Sat, 22 Feb 2020 16:58:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F90E20707 for ; Sat, 22 Feb 2020 16:58:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582390725; bh=gkjFs/1a+pJHG97GNGxiu0bTzUWm8c+N+Zh6h+i2bpY=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=a0bQfy79/5eb3yBmKr58ZngkTpxY4nRS6jCK0oTOLMJEIlUt/gr5n4Umk/Lenr7oS fef3eN5uExZH95ZefR9cxIiCOmYomq2+N7EOjNFkqwMfIKKy18L8kKq+0XoSsOI/Lt A2G3UWFjeyFs74Ru2x90VOCASpHq8/Me7IxAvgtg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726826AbgBVQ6n (ORCPT ); Sat, 22 Feb 2020 11:58:43 -0500 Received: from mail.kernel.org ([198.145.29.99]:56410 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726310AbgBVQ6m (ORCPT ); Sat, 22 Feb 2020 11:58:42 -0500 Received: from localhost (mobile-166-175-186-165.mycingular.net [166.175.186.165]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D8BBF20702; Sat, 22 Feb 2020 16:58:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582390722; bh=gkjFs/1a+pJHG97GNGxiu0bTzUWm8c+N+Zh6h+i2bpY=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=1g1mqO0MCzSViG9n4r2G+9mRMtxkY+CMmvJJt9rUAPfG17iazzt2KeWAsjnYAzzkk e6oc/woJRK+lLRz2SU/p6BFtUwXexTix4uUDruhnWMIlSmbrxG07v/LMs5VKADBn33 SREmsw7MAfw1SBcwAdy54eZ9Ouvf7ImAjKGEXOz0= Date: Sat, 22 Feb 2020 10:58:40 -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 Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification" Message-ID: <20200222165840.GA214760@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200115221008.GA191037@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org [+cc Christoph, Lucas, Dave, Ben, Alex, Myron] 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. > 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