Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth
 notification"
To:     Sinan Kaya <okaya@kernel.org>, Bjorn Helgaas <helgaas@kernel.org>,
        Alexandru Gagniuc <alex_gagniuc@dellteam.com>,
        Keith Busch <keith.busch@intel.com>
Cc:     Jan Vesely <jano.vesely@gmail.com>, Lukas Wunner <lukas@wunner.de>,
        Alex Williamson <alex.williamson@redhat.com>,
        Austin Bolen <austin_bolen@dell.com>,
        Shyam Iyer <Shyam_Iyer@dell.com>, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        Lucas Stach <l.stach@pengutronix.de>,
        Dave Airlie <airlied@gmail.com>,
        Ben Skeggs <skeggsb@gmail.com>,
        Alex Deucher <alexdeucher@gmail.com>,
        Myron Stowe <myron.stowe@redhat.com>,
        "A. Vladimirov" <vladimirov.atanas@gmail.com>
References: <20210128233929.GA39660@bjorn-Precision-5520>
 <6bfe3128-4f4d-6447-ab91-1bc54a02e16f@kernel.org>
From:   "Alex G." <mr.nuke.me@gmail.com>
Message-ID: <f6106d30-cbdb-6ba5-8910-086cee92875e@gmail.com>
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

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