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From: Bjorn Helgaas <helgaas@kernel.org>
To: Alexandru Gagniuc <mr.nuke.me@gmail.com>,
	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>, Sinan Kaya <okaya@kernel.org>,
	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>
Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification"
Date: Sat, 22 Feb 2020 10:58:40 -0600	[thread overview]
Message-ID: <20200222165840.GA214760@google.com> (raw)
In-Reply-To: <20200115221008.GA191037@google.com>

[+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

  parent reply	other threads:[~2020-02-22 16:58 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-15 22:10 Issues with "PCI/LINK: Report degraded links via link bandwidth notification" Bjorn Helgaas
2020-01-16  2:44 ` Alex G
2020-01-18  0:18   ` Bjorn Helgaas
2020-01-20  2:33 ` Bjorn Helgaas
2020-01-20 15:56   ` Alex Williamson
2020-01-20 16:01   ` Alex G.
2020-01-21 11:10     ` Lucas Stach
2020-01-21 14:55       ` Alex G.
2020-02-03  1:56       ` Dave Airlie
2020-02-03  2:04         ` Dave Airlie
2020-02-03  2:07           ` Ben Skeggs
2020-02-03 21:16           ` Alex Deucher
2020-02-04  4:38             ` Lukas Wunner
2020-02-04 14:47               ` Alex Deucher
2020-01-30 16:26   ` Christoph Hellwig
2020-02-22 16:58 ` Bjorn Helgaas [this message]
2021-01-28 23:39   ` Bjorn Helgaas
2021-01-28 23:51     ` Sinan Kaya
2021-01-29  0:07       ` Alex G.
2021-01-29 21:56         ` Bjorn Helgaas
2021-02-02 19:50           ` Alex G.
2021-02-02 20:16             ` Bjorn Helgaas
2021-02-02 20:25               ` Alex G.
2021-01-29  1:30     ` Alex Deucher

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