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
next prev 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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