[kronosnet/kronosnet] 718d1e: [PMTUd] fix external API and PMTUd interaction - Commits

17 Dec 2017

  Branch: refs/heads/mtu-lock
  Home:   https://github.com/kronosnet/kronosnet
  Commit: 718d1e80b56677a1cffe28be2deb25f994062cbe

https://github.com/kronosnet/kronosnet/commit/718d1e80b56677a1cffe28be2deb2…
  Author: Fabio M. Di Nitto &lt;fdinitto(a)redhat.com&gt;
  Date:   2017-12-17 (Sun, 17 Dec 2017)

  Changed paths:
    M libknet/handle.c
    M libknet/host.c
    M libknet/internals.h
    M libknet/links.c
    M libknet/logging.c
    M libknet/tests/Makefile.am
    M libknet/threads_common.c
    M libknet/threads_common.h
    M libknet/threads_dsthandler.c
    M libknet/threads_pmtud.c
    M libknet/transport_sctp.c
    M libknet/transports.c

  Log Message:
  -----------
  [PMTUd] fix external API and PMTUd interaction

The problem:

PMTUd can take a long time to release the global read lock, mostly due
to the pthread_cond_timedwait required to ack/nack packets from the
other hosts. This delay could block any wrlock operation for several seconds
if not more.

The solution:

each call to the global pthread_rwlock_wrlock has been changed to a wrapper
that will notify the PMTUd to interrupt its operations (and restart) first,
then get a global write lock that is queued as soon as PMTUd is going out.

This solution also improves a lot shutdown speed.

How to test:

This is not super simple to test and verify. I used 2 VMs with known MTU of
1500. Start knet_bench on both (normal ping_data -C is more than enough).
Once they have established data exchange, change the MTU on one of the nodes
to 1600 (or higher). This should guarantee that the PMTUd process will take
a very long time to complete.
First verify that the PMTUd process takes several seconds.
Once the next PMTUd run starts, hit ctrl+c on the node that is executing
the PMTUd and the process should exit much faster than before this patch.

Signed-off-by: Fabio M. Di Nitto &lt;fdinitto(a)redhat.com&gt;