[nvidia] Skip SAI discovery on ports (sonic-net#1524)

Given that modern systems have lots of ports, performing SAI discovery takes very long time, e.g. (8 sec) for 256 port system. This has a big impact of fast-boot downtime and the discovery itself is not required for Nvidia platform fast-boot.

Same applies to Nvidia fastfast-boot (aka warm-boot), yet needs to be tested separately.

Author: mssonicbld

syncd/Makefile.am

@@ -82,6 +82,10 @@ if SONIC_ASIC_PLATFORM_BROADCOM
 libSyncd_a_CXXFLAGS += -DMDIO_ACCESS_USE_NPU
 endif
 
+if SONIC_ASIC_PLATFORM_MELLANOX
+libSyncd_a_CPPFLAGS += -DSKIP_SAI_PORT_DISCOVERY
+endif
+
 libSyncdRequestShutdown_a_SOURCES = \
 									RequestShutdown.cpp \
 									RequestShutdownCommandLineOptions.cpp \

syncd/SaiDiscovery.cpp

@@ -87,6 +87,13 @@ void SaiDiscovery::discover(
         discovered.insert(rid);
     }
 
+#ifdef SKIP_SAI_PORT_DISCOVERY
+    if (ot == SAI_OBJECT_TYPE_PORT)
+    {
+        return;
+    }
+#endif
+
     const sai_object_type_info_t *info = sai_metadata_get_object_type_info(ot);
 
     /*

syncd/Syncd.cpp

@@ -223,6 +223,10 @@ Syncd::Syncd(
 
     m_breakConfig = BreakConfigParser::parseBreakConfig(m_commandLineOptions->m_breakConfig);
 
+#ifdef SKIP_SAI_PORT_DISCOVERY
+    SWSS_LOG_WARN("SAI discovery is skipped on ports");
+#endif
+
     SWSS_LOG_NOTICE("syncd started");
 }