linux-pci.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Alex Williamson <alex.williamson@redhat.com>
To: Alex G <mr.nuke.me@gmail.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
	linux-pci@vger.kernel.org, austin_bolen@dell.com,
	alex_gagniuc@dellteam.com, keith.busch@intel.com,
	Shyam_Iyer@Dell.com, lukas@wunner.de, okaya@kernel.org,
	torvalds@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PCI/LINK: Account for BW notification in vector calculation
Date: Tue, 23 Apr 2019 12:38:28 -0600	[thread overview]
Message-ID: <20190423123828.691bb37c@x1.home> (raw)
In-Reply-To: <9802ef46-40d2-b83c-a0c6-8bd6ac25feaa@gmail.com>

On Tue, 23 Apr 2019 12:53:07 -0500
Alex G <mr.nuke.me@gmail.com> wrote:

> On 4/23/19 12:10 PM, Bjorn Helgaas wrote:
> > On Tue, Apr 23, 2019 at 09:33:53AM -0500, Alex G wrote:  
> >> On 4/22/19 7:33 PM, Alex Williamson wrote:  
> >>> There is nothing wrong happening here that needs to fill logs.  I
> >>> thought maybe if I enabled notification of autonomous bandwidth
> >>> changes that it might categorize these as something we could
> >>> ignore, but it doesn't.  How can we identify only cases where this
> >>> is an erroneous/noteworthy situation?  Thanks,  
> >>
> >> You don't. Ethernet doesn't. USB doesn't. This logging behavior is
> >> consistent with every other subsystem that deals with multi-speed links.  
> > 
> > Can you point me to the logging in these other subsystems so I can
> > learn more about how they deal with this?  
> 
> I don't have any in-depth articles about the logging in these systems, 
> but I can extract some logs from my machines.
> 
> Ethernet:
> 
> [Sun Apr 21 11:14:06 2019] e1000e: eno1 NIC Link is Down
> [Sun Apr 21 11:14:17 2019] e1000e: eno1 NIC Link is Up 1000 Mbps Full 
> Duplex, Flow Control: Rx/Tx
> [Sun Apr 21 11:14:23 2019] e1000e: eno1 NIC Link is Up 1000 Mbps Full 
> Duplex, Flow Control: Rx/Tx
> [Sun Apr 21 23:33:31 2019] e1000e: eno1 NIC Link is Down
> [Sun Apr 21 23:33:43 2019] e1000e: eno1 NIC Link is Up 1000 Mbps Full 
> Duplex, Flow Control: Rx/Tx
> [Sun Apr 21 23:33:48 2019] e1000e: eno1 NIC Link is Up 1000 Mbps Full 
> Duplex, Flow Control: Rx/Tx
> 
> I used to have one of these "green" ethernet switches that went down to 
> 100mbps automatically. You can imagine how "clogged" the logs were with 
> link up messages. Thank goodness that switch was killed in a thunderstorm.
> 
> USB will log every device insertion and removal, very verbosely (see 
> appendix A).

I have a hard time putting USB insertion and removal into the same
class, the equivalent is PCI hotplug which is logged separately.  Do
we ever log beyond USB device discovery if a device is running at a
lower speed than is possible?  The most directly related is the green
ethernet switch, which you admit was a nuisance due to exactly this
sort of logging.  It was probably confusing to see this logging, perhaps
you wondered if the cable was bad or the switch was defective.

> > I agree that emitting log messages for normal and expected events will
> > lead to user confusion and we need to do something.
> > 
> > e8303bb7a75c ("PCI/LINK: Report degraded links via link bandwidth
> > notification") was merged in v5.1-rc1, so we still have (a little)
> > time to figure this out before v5.1.  
> 
> I always viewed the system log as a system log, instead of a database of 
> system errors. I may have extremist views, but going back to Alex's 
> example, I prefer to see that the power saving mechanism is doing 
> something to save power on my laptop (I'll just ignore it on a desktop).

There's a disconnect from above where similar behavior on ethernet
behavior "clogged" the log files, but here we just want to ignore it.
Excessive logging can also be considered a denial of service vector
when the device generating that excessive logging is attached to a
userspace driver.

> If you think increasing code complexity because people don't want things 
> logged into the system log, then I'm certain we can work out some sane 
> solution. It's the same problem we see with GCC, where people want 
> warning messages here, but don't want the same messages there.

v5.1 is approaching quickly, can we downgrade these to pci_dbg() while
we work on maybe some sort of driver participation in this logging?
Thanks,

Alex

  reply	other threads:[~2019-04-23 18:38 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-22 22:43 Alex Williamson
2019-04-23  0:05 ` Alex G
2019-04-23  0:33   ` Alex Williamson
2019-04-23 14:33     ` Alex G
2019-04-23 15:34       ` Alex Williamson
2019-04-23 15:49         ` Lukas Wunner
2019-04-23 16:03         ` Alex G
2019-04-23 16:22           ` Alex Williamson
2019-04-23 16:27             ` Alex G
2019-04-23 16:37               ` Alex Williamson
2019-04-23 17:10       ` Bjorn Helgaas
2019-04-23 17:53         ` Alex G
2019-04-23 18:38           ` Alex Williamson [this message]
2019-04-23 17:59 ` Alex G
2019-05-01 20:30 ` Bjorn Helgaas

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190423123828.691bb37c@x1.home \
    --to=alex.williamson@redhat.com \
    --cc=Shyam_Iyer@Dell.com \
    --cc=alex_gagniuc@dellteam.com \
    --cc=austin_bolen@dell.com \
    --cc=helgaas@kernel.org \
    --cc=keith.busch@intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --cc=lukas@wunner.de \
    --cc=mr.nuke.me@gmail.com \
    --cc=okaya@kernel.org \
    --cc=torvalds@linux-foundation.org \
    --subject='Re: [PATCH] PCI/LINK: Account for BW notification in vector calculation' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).