FAQ: Add question on Packet loss with RFC2544 tests

Signed-off-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy@intel.com>
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>

diff --git a/FAQ.md b/FAQ.md
index 2f50b9615d96b24f5ea9c5ac4524af93552c90ab..f4fd55da7d27b4e16d5c6863e23e26927c98728a 100644 (file)
--- a/FAQ.md
+++ b/FAQ.md
@@ -1051,6 +1051,19 @@ A: The short answer is that this is a misuse of a "tap" device.  Use
    users should not configure KVM "tap" devices as type "tap" (use
    type "system", the default, instead).
 
+### Q: I observe packet loss at the beginning of RFC2544 tests on a
+    server running few hundred container apps bridged to OVS with traffic
+    generated by HW traffic generator.  How can I fix this?
+
+A: This is expected behavior on virtual switches.  RFC2544 tests were
+   designed for hardware switches, which don't have caches on the fastpath
+   that need to be heated.  Traffic generators in order to prime the switch
+   use learning phase to heat the caches before sending the actual traffic
+   in test phase.  In case of OVS the cache is flushed quickly and to
+   accommodate the traffic generator's delay between learning and test phase,
+   the max-idle timeout settings should be changed to 50000 ms.
+
+   ovs-vsctl --no-wait set Open_vSwitch . other_config:max-idle=50000
 
 ## QOS