Bug 1271341

+++ This bug was initially created as a clone of Bug #1269613 +++

On a test system with 514 bridges each having an attach vlan interface, "virsh iface-dumpxml" of all toplevel interfaces takes 13min46sec. This is a bad thing because that's essentially what virt-manager does every time it is started.

Investigation and upstream discussion on the netcf-devel and augeas-devel mailing lists:

  https://www.redhat.com/archives/augeas-devel/2015-September/msg00001.html
  https://www.redhat.com/archives/augeas-devel/2015-October/msg00000.html

led to the following:

1) Several commits have recently been pushed to upstream augeas (post 1.4.0) which end up having a dramatic effect on the execution time of "virsh iface-dumpxml" for all interfaces on a system with 514 bridges + 514 vlans. Here are the augeas upstream commit IDs:

  commit a659f09afa1d6383d17a724da9c2ddbb77f844a7
  Author: David Lutterkort <lutter>
  Date:   Mon Sep 28 14:37:03 2015 -0700

    Speed up the duplicate check when constructing nodesets
    
  commit 41e989ca1f9abf7a13e0f333e90857f2ccafbf7d
  Author: David Lutterkort <lutter>
  Date:   Mon Sep 28 14:51:42 2015 -0700

    * src/pathx.c (ns_filter): speed up by removing nodes in batches
    
  commit 23d5e480cab312ed3f47f9f6e0777b152d6df9df
  Author: David Lutterkort <lutter>
  Date:   Mon Sep 28 15:40:31 2015 -0700

    * src/pathx.c (ns_from_locpath): special-case 'name[42]' path expressions

These reduce the time from 13m46s to 7m34s! (The netcf patch given in Bug 1268382 further reduces this time to 6m40s).

2) There is an aug_match() query in netcf that takes a *very* long time to complete (nearly 1 second for each query!). It is in drv_redhat.c:

    ndevs = aug_fmt_match(ncf, &devs,
              "%s[ DEVICE = '%s' or BRIDGE = '%s' or MASTER = '%s'"
              "    or MASTER = ../*[BRIDGE = '%s']/DEVICE" ]/DEVICE",
              ifcfg_path, nif->name, nif->name, nif->name, nif->name);

So the query expression is, e.g.:

     "/files/etc/sysconfig/network-scripts/*[ "
     "DEVICE = 'br1' or BRIDGE = 'br1' or MASTER = 'br1' or MASTER = "
     "../*[BRIDGE = 'br1']/DEVICE ]/DEVICE"

The time-consuming part is the final term:

     MASTER = ../*[BRIDGE='br1']DEVICE

This searches for all ifcfg files that have a MASTER that is equal to the DEVICE name of any other ifcfg file that has BRIDGE='br1'. David Lutterkort has offered some advice on how to rewrite that query to make it much more efficient:

  https://www.redhat.com/archives/augeas-devel/2015-October/msg00003.html

  "(/files/etc/sysconfig/network-scripts/*[(DEVICE|BRIDGE|MASTER) = '%s']"
  "|/files/etc/sysconfig/network-scripts/*[MASTER]"
  "[MASTER = ../*[BRIDGE = '%s']/DEVICE ])/DEVICE

I've implemented that in a netcf patch, and it reduces the time for virsh iface-dumpxml of all interfaces from 6m40s down to 17 seconds.

--- Additional comment from Laine Stump on 2015-10-13 13:04:58 EDT ---

This is the upstream patch that changes the query and reduces time (in the specific test case) from 6m40s to 17s:

commit 396e4e0698d9fb542f2eb8b32790a069e1c0df61
Author: Laine Stump <laine>
Date:   Wed Oct 7 13:49:45 2015 -0400

    optimize aug_match() query for all ifcfg files related to an interface