[Bug 1745597] Re: mii-monitor-interval unit is undocumented, and may be wrong

[Mathieu Trudel-Lapierre]

** This bug is no longer a duplicate of bug 1765833
   bond intervals default to seconds; breaks existing configs

** Also affects: nplan (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: nplan (Ubuntu)
       Status: New => Fix Released

** Changed in: netplan
       Status: In Progress => Fix Released

** Also affects: nplan (Ubuntu Artful)
   Importance: Undecided
       Status: New

** Also affects: nplan (Ubuntu Xenial)
   Importance: Undecided
       Status: New

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Title:
  mii-monitor-interval unit is undocumented, and may be wrong

Status in netplan:
  Fix Released
Status in nplan package in Ubuntu:
  Fix Released
Status in nplan source package in Xenial:
  New
Status in nplan source package in Artful:
  New

Bug description:
  [Impact]
  Users of bond and bridges devices requiring tuning of the default device parameters.

  [Test case]
  == Configure MII monitor interval ==
  1) Configure a bond device
  2) Add parameters:

  bonds:
    mybond0:
      parameters:
        mii-monitor-interval: 1

  3) Verify that the applied MII monitor interval is of 1ms, as opposed
  to 1 second (1000ms), by verifying the contents of
  /sys/class/net/mybond0/bonding/miimon

  
  == Validate default behavior ==
  1) Configure a bond device without parameters.
  2) Verify that no special MII monitor interval is applied, the default value should be 0:

  $ cat /sys/class/net/mybond0/bonding/miimon
  0

  
  [Regression potential]
  MII monitor behavior is changing with this SRU. Default behavior for an unqualified value (ie. a number alone), which was also the only way to specify parameters, was to interpret the values as *seconds*. This leads to relatively slow checking of the device link status (for MII monitor), much slower than generally expected. The same applies to other time-based values such as up delay, down delay, arp interval. The interpretation for these values changes to reading them as *milliseconds* when unqualified, and a new way of qualifying the values (adding a modifier) was added. This was, people who do require "slow" checking of the MII link status will be migrated to "fast" checking right now, moving from an interval of 1 second to 1 millisecond (more checking means less false-negatives for packet passing through an interface, should reduce packet loss, at the cost of potentially flapping the interfaces (bringing down a path often if MII status is bad or slow to be returned)). Users who require the old behavior may add "s" at the end of the value to make it read as "1 second" again, or modify the value to be "1000", which will be 1000ms (1 second). We estimate the impact of this change to users to be minimal,  actually requiring a 1 second interval for MII monitoring / up/down delay, and ARP interval is very uncommon and counter-intuitive as all other systems work on a millisecond basis.

  ---

  The manpage for netplan doesn't indicate what the unit for mii-
  monitor-interval is on bond devices. It appears to be in whole
  seconds, but at the kernel level, the unit is milliseconds.

  From my testing, it appears to be impossible to set a value for mii-
  monitor-interval with netplan that is <1s (e.g. I got a syntax error
  with a value of 0.1 for 100ms)

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