RFNoC: Disable FC ACK packets for lossless links

FC ACK packets are unnecessary on lossless links and degrade overall
performance.  This change disables those packets on all lossless links.

Signed-off-by: Michael West <michael.west@ettus.com>

5 files changed, 25 insertions, 15 deletions

diff --git a/host/include/uhd/rfnoc/constants.hpp b/host/include/uhd/rfnoc/constants.hpp
index 3e67a3cae..2bef70a75 100644
--- a/host/include/uhd/rfnoc/constants.hpp
+++ b/host/include/uhd/rfnoc/constants.hpp
@@ -25,7 +25,7 @@ static const std::string XML_PATH_ENV = "UHD_RFNOC_DIR";
 static const std::string DEFAULT_BLOCK_NAME = "Block";
 static const uint64_t DEFAULT_NOC_ID        = 0xFFFFFFFFFFFFFFFF;
 static const size_t NOC_SHELL_COMPAT_MAJOR  = 5;
-static const size_t NOC_SHELL_COMPAT_MINOR  = 0;
+static const size_t NOC_SHELL_COMPAT_MINOR  = 1;
 
 static const size_t MAX_PACKET_SIZE     = 8000; // bytes
 static const size_t DEFAULT_PACKET_SIZE = 1456; // bytes
diff --git a/host/include/uhd/rfnoc/source_block_ctrl_base.hpp b/host/include/uhd/rfnoc/source_block_ctrl_base.hpp
index c0a8494c1..a22a19da9 100644
--- a/host/include/uhd/rfnoc/source_block_ctrl_base.hpp
+++ b/host/include/uhd/rfnoc/source_block_ctrl_base.hpp
@@ -102,15 +102,17 @@ public:
      * disables byte based flow control. If both byte based flow control and the packet
      * limit are set to zero, the block will then produce data as fast as it can. \b
      * Warning: This can cause head-of-line blocking, and potentially lock up your device!
-     * \param pkt_limit Limit the maximum number of packets in flight. Setting this to
-     * zero disables packet limiting. Usually kept disabled except for special case
-     * connections (such as DMA) that support only a finite number of packets in flight.
-     * \param block_port Specify on which outgoing port this setting is valid.
-     * \param sid The SID for which this is valid. This is meant for cases where the
-     * outgoing block port is not sufficient to set the flow control, and as such is
+     * \param lossless_link The link for the connection is lossless.  Periodic sync
+     * packets will be disabled. \param pkt_limit Limit the maximum number of packets in
+     * flight. Setting this to zero disables packet limiting. Usually kept disabled except
+     * for special case connections (such as DMA) that support only a finite number of
+     * packets in flight. \param block_port Specify on which outgoing port this setting is
+     * valid. \param sid The SID for which this is valid. This is meant for cases where
+     * the outgoing block port is not sufficient to set the flow control, and as such is
      * rarely used.
      */
     virtual void configure_flow_control_out(const bool enable_output,
+        const bool lossless_link,
         const size_t buf_size_bytes,
         const size_t pkt_limit  = 0,
         const size_t block_port = 0,
diff --git a/host/lib/rfnoc/graph_impl.cpp b/host/lib/rfnoc/graph_impl.cpp
index 989bcb0c4..326e9205d 100644
--- a/host/lib/rfnoc/graph_impl.cpp
+++ b/host/lib/rfnoc/graph_impl.cpp
@@ -120,17 +120,17 @@ void graph_impl::connect(const block_id_t& src_block,
                 % dst->get_block_id().get() % (dst->get_fifo_size(dst_block_port) / 1024)
                 % (pkt_size / 1024) % src->get_block_id().get()));
     }
+    const bool same_xbar = sid.get_src_addr() == sid.get_dst_addr();
     src->configure_flow_control_out(true, /* enable output */
+        same_xbar, // Lossless link if on same crossbar
         buf_size_bytes,
         0, /* no packet limit. We need to revisit this at some point. */
         src_block_port);
     // On the same crossbar, use lots of FC packets
-    size_t bytes_per_response =
-        buf_size_bytes / uhd::rfnoc::DEFAULT_FC_XBAR_RESPONSE_FREQ;
     // Over the network, use less or we'd flood the transport
-    if (sid.get_src_addr() != sid.get_dst_addr()) {
-        bytes_per_response = buf_size_bytes / uhd::rfnoc::DEFAULT_FC_TX_RESPONSE_FREQ;
-    }
+    const size_t bytes_per_response =
+        same_xbar ? buf_size_bytes / uhd::rfnoc::DEFAULT_FC_XBAR_RESPONSE_FREQ
+                  : buf_size_bytes / uhd::rfnoc::DEFAULT_FC_TX_RESPONSE_FREQ;
     UHD_ASSERT_THROW(bytes_per_response != 0);
     dst->configure_flow_control_in(bytes_per_response, dst_block_port);
 
@@ -189,7 +189,12 @@ void graph_impl::connect_src(const block_id_t& src_block,
                 % (buf_size_dst_bytes / 1024) % (pkt_size / 1024)
                 % src->get_block_id().get()));
     }
-    src->configure_flow_control_out(buf_size_pkts, src_block_port);
+
+    src->configure_flow_control_out(true, /* enable output */
+        (dst_sid.get_src_addr() == dst_sid.get_dst_addr()),
+        buf_size_dst_bytes,
+        0, /* no packet limit. We need to revisit this at some point. */
+        src_block_port);
 }
 
 void graph_impl::connect_sink(
diff --git a/host/lib/rfnoc/source_block_ctrl_base.cpp b/host/lib/rfnoc/source_block_ctrl_base.cpp
index 6c41fae14..656ab26af 100644
--- a/host/lib/rfnoc/source_block_ctrl_base.cpp
+++ b/host/lib/rfnoc/source_block_ctrl_base.cpp
@@ -86,6 +86,7 @@ void source_block_ctrl_base::set_destination(
 }
 
 void source_block_ctrl_base::configure_flow_control_out(const bool enable_fc_output,
+    const bool lossless_link,
     const size_t buf_size_bytes,
     const size_t pkt_limit,
     const size_t block_port,
@@ -124,8 +125,9 @@ void source_block_ctrl_base::configure_flow_control_out(const bool enable_fc_out
     // count based flow control
     const bool enable_byte_fc    = (buf_size_bytes != 0);
     const bool enable_pkt_cnt_fc = (pkt_limit != 0);
-    const uint32_t config        = (enable_fc_output ? 1 : 0) | (enable_byte_fc << 1)
-                            | (enable_pkt_cnt_fc << 2);
+    const uint32_t config = (enable_fc_output ? 1 : 0) | ((enable_byte_fc ? 1 : 0) << 1)
+                            | ((enable_pkt_cnt_fc ? 1 : 0) << 2)
+                            | ((lossless_link ? 1 : 0) << 3);
 
     // Resize the FC window.
     // Precondition: No data can be buffered upstream.
diff --git a/host/lib/usrp/device3/device3_io_impl.cpp b/host/lib/usrp/device3/device3_io_impl.cpp
index 2bc59f1a8..ce8ff2cbf 100644
--- a/host/lib/usrp/device3/device3_io_impl.cpp
+++ b/host/lib/usrp/device3/device3_io_impl.cpp
@@ -357,6 +357,7 @@ rx_streamer::sptr device3_impl::get_rx_stream(const stream_args_t& args_)
         UHD_RX_STREAMER_LOG() << "Flow Control Window = " << (fc_window)
                               << ", Flow Control Handler Window = " << fc_handle_window;
         blk_ctrl->configure_flow_control_out(true,
+            xport.lossless,
             fc_window,
             rx_hints.cast<size_t>("recv_pkt_limit",
                 0), // On rfnoc-devel, update e300_impl::get_rx_hints() to set this to 32