dpif-netdev: Detection and logging of suspicious PMD iterations

This patch enhances dpif-netdev-perf to detect iterations with
suspicious statistics according to the following criteria:

- iteration lasts longer than US_THR microseconds (default 250).
  This can be used to capture events where a PMD is blocked or
  interrupted for such a period of time that there is a risk for
  dropped packets on any of its Rx queues.

- max vhost qlen exceeds a threshold Q_THR (default 128). This can
  be used to infer virtio queue overruns and dropped packets inside
  a VM, which are not visible in OVS otherwise.

Such suspicious iterations can be logged together with their iteration
statistics to be able to correlate them to packet drop or other events
outside OVS.

A new command is introduced to enable/disable logging at run-time and
to adjust the above thresholds for suspicious iterations:

ovs-appctl dpif-netdev/pmd-perf-log-set on | off
    [-b before] [-a after] [-e|-ne] [-us usec] [-q qlen]

Turn logging on or off at run-time (on|off).

-b before:  The number of iterations before the suspicious iteration to
            be logged (default 5).
-a after:   The number of iterations after the suspicious iteration to
            be logged (default 5).
-e:         Extend logging interval if another suspicious iteration is
            detected before logging occurs.
-ne:        Do not extend logging interval (default).
-q qlen:    Suspicious vhost queue fill level threshold. Increase this
            to 512 if the Qemu supports 1024 virtio queue length.
            (default 128).
-us usec:   change the duration threshold for a suspicious iteration
            (default 250 us).

Note: Logging of suspicious iterations itself consumes a considerable
amount of processing cycles of a PMD which may be visible in the iteration
history. In the worst case this can lead OVS to detect another
suspicious iteration caused by logging.

If more than 100 iterations around a suspicious iteration have been
logged once, OVS falls back to the safe default values (-b 5/-a 5/-ne)
to avoid that logging itself causes continuos further logging.

Signed-off-by: Jan Scheurich <jan.scheurich@ericsson.com>
Acked-by: Billy O'Mahony <billy.o.mahony@intel.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>

lib/dpif-netdev-unixctl.man

@@ -149,6 +149,65 @@ reported by the \fBdpif-netdev/pmd-stats-show\fR command.
 To reset the counters and start a new measurement use
 \fBdpif-netdev/pmd-stats-clear\fR.
 .
+.IP "\fBdpif-netdev/pmd-perf-log-set\fR \fBon\fR|\fBoff\fR \
+[\fB-b\fR \fIbefore\fR] [\fB-a\fR \fIafter\fR] [\fB-e\fR|\fB-ne\fR] \
+[\fB-us\fR \fIusec\fR] [\fB-q\fR \fIqlen\fR]"
+.
+The userspace "netdev" datapath is able to supervise the PMD performance
+metrics and detect iterations with suspicious statistics according to the
+following criteria:
+.RS
+.IP \(em
+The iteration lasts longer than \fIusec\fR microseconds (default 250).
+This can be used to capture events where a PMD is blocked or interrupted for
+such a period of time that there is a risk for dropped packets on any of its Rx
+queues.
+.IP \(em
+The max vhost qlen exceeds a threshold \fIqlen\fR (default 128). This can be
+used to infer virtio queue overruns and dropped packets inside a VM, which are
+not visible in OVS otherwise.
+.RE
+.IP
+Such suspicious iterations can be logged together with their iteration
+statistics in the \fBovs-vswitchd.log\fR to be able to correlate them to
+packet drop or other events outside OVS.
+
+The above command enables (\fBon\fR) or disables (\fBoff\fR) supervision and
+logging at run-time and can be used to adjust the above thresholds for
+detecting suspicious iterations. By default supervision and logging is
+disabled.
+
+The command options are:
+.RS
+.IP "\fB-b\fR \fIbefore\fR"
+The number of iterations before the suspicious iteration to be logged
+(default 5).
+.IP "\fB-a\fR \fIafter\fR"
+The number of iterations after the suspicious iteration to be logged
+(default 5).
+.IP "\fB-e\fR"
+Extend logging interval if another suspicious iteration is detected
+before logging occurs.
+.IP "\fB-ne\fR"
+Do not extend logging interval if another suspicious iteration is detected
+before logging occurs (default).
+.IP "\fB-q\fR \fIqlen\fR"
+Suspicious vhost queue fill level threshold. Increase this to 512 if the Qemu
+supports 1024 virtio queue length (default 128).
+.IP "\fB-us\fR \fIusec\fR"
+Change the duration threshold for a suspicious iteration (default 250 us).
+.RE
+
+Note: Logging of suspicious iterations itself consumes a considerable amount
+of processing cycles of a PMD which may be visible in the iteration history.
+In the worst case this can lead OVS to detect another suspicious iteration
+caused by logging.
+
+If more than 100 iterations around a suspicious iteration have been logged
+once, OVS falls back to the safe default values (-b 5 -a 5 -ne) to avoid
+that logging itself continuously causes logging of further suspicious
+iterations.
+.
 .IP "\fBdpif-netdev/pmd-rxq-show\fR [\fB-pmd\fR \fIcore\fR] [\fIdp\fR]"
 For one or all pmd threads of the datapath \fIdp\fR show the list of queue-ids
 with port names, which this thread polls.