dpif-netdev: Add PMD load based sleeping.

Sleep for an incremental amount of time if none of the Rx queues
assigned to a PMD have at least half a batch of packets (i.e. 16 pkts)
on an polling iteration of the PMD.

Upon detecting the threshold of >= 16 pkts on an Rxq, reset the
sleep time to zero (i.e. no sleep).

Sleep time will be increased on each iteration where the low load
conditions remain up to a total of the max sleep time which is set
by the user e.g:
ovs-vsctl set Open_vSwitch . other_config:pmd-maxsleep=500

The default pmd-maxsleep value is 0, which means that no sleeps
will occur and the default behaviour is unchanged from previously.

Also add new stats to pmd-perf-show to get visibility of operation
e.g.
...
   - sleep iterations:       153994  ( 76.8 % of iterations)
   Sleep time (us):         9159399  ( 59 us/iteration avg.)
...

Reviewed-by: Robin Jarry <rjarry@redhat.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Kevin Traynor <ktraynor@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
index f9bdb2d92..8c4acfb18 100644
--- a/vswitchd/vswitch.xml
+++ b/vswitchd/vswitch.xml
@@ -788,6 +788,32 @@
          The default value is <code>25%</code>.
         </p>
       </column>
+      <column name="other_config" key="pmd-maxsleep"
+              type='{"type": "integer",
+                     "minInteger": 0, "maxInteger": 10000}'>
+        <p>
+          Specifies the maximum sleep time that will be requested in
+          microseconds per iteration for a PMD thread which has received zero
+          or a small amount of packets from the Rx queues it is polling.
+        </p>
+        <p>
+          The actual sleep time requested is based on the load
+          of the Rx queues that the PMD polls and may be less than
+          the maximum value.
+        </p>
+        <p>
+          The default value is <code>0 microseconds</code>, which means
+          that the PMD will not sleep regardless of the load from the
+          Rx queues that it polls.
+        </p>
+        <p>
+          To avoid requesting very small sleeps (e.g. less than 10 us) the
+          value will be rounded up to the nearest 10 us.
+        </p>
+        <p>
+          The maximum value is <code>10000 microseconds</code>.
+        </p>
+      </column>
       <column name="other_config" key="userspace-tso-enable"
               type='{"type": "boolean"}'>
         <p>