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[98.195.139.126]) by smtp.gmail.com with ESMTPSA id r1sm1610314ooq.16.2021.01.28.16.07.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Jan 2021 16:07:38 -0800 (PST) Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification" To: Sinan Kaya , Bjorn Helgaas , Alexandru Gagniuc , Keith Busch Cc: Jan Vesely , Lukas Wunner , Alex Williamson , Austin Bolen , Shyam Iyer , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Lucas Stach , Dave Airlie , Ben Skeggs , Alex Deucher , Myron Stowe , "A. Vladimirov" References: <20210128233929.GA39660@bjorn-Precision-5520> <6bfe3128-4f4d-6447-ab91-1bc54a02e16f@kernel.org> From: "Alex G." Message-ID: Date: Thu, 28 Jan 2021 18:07:36 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <6bfe3128-4f4d-6447-ab91-1bc54a02e16f@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 1/28/21 5:51 PM, Sinan Kaya wrote: > On 1/28/2021 6:39 PM, Bjorn Helgaas wrote: >> 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. > > Hide behind debug or expert option by default? or even mark it as BROKEN > until someone fixes it? > Instead of making it a config option, wouldn't it be better as a kernel parameter? People encountering this seem quite competent in passing kernel arguments, so having a "pcie_bw_notification=off" would solve their problems. As far as marking this as broken, I've seen no conclusive evidence of to tell if its a sw bug or actual hardware problem. Could we have a sysfs to disable this on a per-downstream-port basis? e.g. echo 0 > /sys/bus/pci/devices/0000:00:04.0/bw_notification_enabled This probably won't be ideal if there are many devices downtraining their links ad-hoc. At worst we'd have a way to silence those messages if we do encounter such devices. Alex