From: Bjorn Helgaas <helgaas@kernel.org>
To: Alex G <mr.nuke.me@gmail.com>
Cc: Alexandru Gagniuc <alex_gagniuc@dellteam.com>,
Keith Busch <keith.busch@intel.com>,
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
Subject: Re: Issues with "PCI/LINK: Report degraded links via link bandwidth notification"
Date: Fri, 17 Jan 2020 18:18:17 -0600 [thread overview]
Message-ID: <20200117234627.GA144414@google.com> (raw)
In-Reply-To: <967fb44c-b1cd-875c-2354-b6ad0b8ae6d7@gmail.com>
On Wed, Jan 15, 2020 at 08:44:21PM -0600, Alex G wrote:
> Hi Bjorn,
>
> I'm no longer working on this, so my memory may not be up to speed. If the
> endpoint is causing the bandwidth change, then we should get an _autonomous_
> link management interrupt instead. I don't think we report those, and that
> shouldn't spam the logs
>
> If it's not a (non-autonomous) link management interrupt, then something is
> causing the downstream port to do funny things. I don't think ASPM is
> supposed to be causing this.
>
> Do we know what's causing these swings?
>
> For now, I suggest a boot-time parameter to disable link speed reporting
> instead of a compile time option.
If we add a parameter, it would have to be that reporting is disabled
by default, and the parameter would enable it. That way the default
will not spam the logs and cause more problem reports.
I don't have time to debug this and I don't like boot parameters in
general, so somebody else will have to step up to resolve this.
At the very least, we need a Kconfig update to warn about the
possibility, and we may need to consider reverting this if we don't
have a better solution.
> On 1/15/20 4:10 PM, 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
> >
> > 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:[~2020-01-18 0:18 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 [this message]
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
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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