Support so_busy_poll (#4188)

* Support so_busy_poll.

CMakeLists.txt

@@ -555,6 +555,7 @@ else()
   check_cxx_symbol_exists(if_nametoindex net/if.h HAVE_IF_NAMETOINDEX)
   check_cxx_symbol_exists(SO_PEERCRED sys/socket.h ZMQ_HAVE_SO_PEERCRED)
   check_cxx_symbol_exists(LOCAL_PEERCRED sys/socket.h ZMQ_HAVE_LOCAL_PEERCRED)
+  check_cxx_symbol_exists(SO_BUSY_POLL sys/socket.h ZMQ_HAVE_BUSY_POLL)
 endif()
 
 if(NOT MINGW)

builds/cmake/platform.hpp.in

@@ -35,6 +35,7 @@
 
 #cmakedefine ZMQ_HAVE_SO_PEERCRED
 #cmakedefine ZMQ_HAVE_LOCAL_PEERCRED
+#cmakedefine ZMQ_HAVE_BUSY_POLL
 
 #cmakedefine ZMQ_HAVE_O_CLOEXEC
 

doc/zmq_setsockopt.txt

@@ -87,6 +87,21 @@ Default value:: not set
 Applicable socket types:: all, when using TCP or UDP transports.
 
 
+ZMQ_BUSY_POLL: This removes delays caused by the interrupt and the resultant context switch.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Busy polling helps reduce latency in the network receive path by allowing socket layer code
+to poll the receive queue of a network device, and disabling network interrupts. This removes
+delays caused by the interrupt and the resultant context switch. However, it also increases
+CPU utilization. Busy polling also prevents the CPU from sleeping, which can incur additional
+power consumption.
+
+[horizontal]
+Option value type:: int
+Option value unit:: 0,1
+Default value:: 0
+Applicable socket types:: all
+
+
 ZMQ_CONNECT_RID: Assign the next outbound connection id
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 This option name is now deprecated. Use ZMQ_CONNECT_ROUTING_ID instead.

include/zmq.h

@@ -683,6 +683,7 @@ ZMQ_EXPORT void zmq_threadclose (void *thread_);
 #define ZMQ_HELLO_MSG 110
 #define ZMQ_DISCONNECT_MSG 111
 #define ZMQ_PRIORITY 112
+#define ZMQ_BUSY_POLL 113
 
 /*  DRAFT ZMQ_RECONNECT_STOP options                                          */
 #define ZMQ_RECONNECT_STOP_CONN_REFUSED 0x1

src/options.cpp

@@ -254,7 +254,8 @@ zmq::options_t::options_t () :
     hello_msg (),
     can_send_hello_msg (false),
     disconnect_msg (),
-    can_recv_disconnect_msg (false)
+    can_recv_disconnect_msg (false),
+    busy_poll (0)
 {
     memset (curve_public_key, 0, CURVE_KEYSIZE);
     memset (curve_secret_key, 0, CURVE_KEYSIZE);
@@ -802,6 +803,12 @@ int zmq::options_t::setsockopt (int option_,
             }
             break;
 
+        case ZMQ_BUSY_POLL:
+            if (is_int) {
+                busy_poll = value;
+                return 0;
+            }
+            break;
 #ifdef ZMQ_HAVE_WSS
         case ZMQ_WSS_KEY_PEM:
             // TODO: check if valid certificate
@@ -1285,6 +1292,12 @@ int zmq::options_t::getsockopt (int option_,
                 return 0;
             }
             break;
+
+        case ZMQ_BUSY_POLL:
+            if (is_int) {
+                *value = busy_poll;
+            }
+            break;
 #endif
 
 

src/options.hpp

@@ -308,6 +308,9 @@ struct options_t
     //  Disconnect msg
     std::vector<unsigned char> disconnect_msg;
     bool can_recv_disconnect_msg;
+
+    //  This option removes several delays caused by scheduling, interrupts and context switching.
+    int busy_poll;
 };
 
 inline bool get_effective_conflate_option (const options_t &options)

src/tcp.cpp

@@ -341,6 +341,21 @@ void zmq::tcp_tune_loopback_fast_path (const fd_t socket_)
 #endif
 }
 
+void zmq::tune_tcp_busy_poll (fd_t socket_, int busy_poll_)
+{
+#if defined(ZMQ_HAVE_BUSY_POLL)
+    if (busy_poll_ > 0) {
+        const int rc =
+          setsockopt (socket_, SOL_SOCKET, SO_BUSY_POLL,
+                      reinterpret_cast<char *> (&busy_poll_), sizeof (int));
+        assert_success_or_recoverable (socket_, rc);
+    }
+#else
+    LIBZMQ_UNUSED (socket_);
+    LIBZMQ_UNUSED (busy_poll_);
+#endif
+}
+
 zmq::fd_t zmq::tcp_open_socket (const char *address_,
                                 const zmq::options_t &options_,
                                 bool local_,
@@ -398,6 +413,9 @@ zmq::fd_t zmq::tcp_open_socket (const char *address_,
     if (options_.rcvbuf >= 0)
         set_tcp_receive_buffer (s, options_.rcvbuf);
 
+    //  This option removes several delays caused by scheduling, interrupts and context switching.
+    if (options_.busy_poll)
+        tune_tcp_busy_poll (s, options_.busy_poll);
     return s;
 
 setsockopt_error:

src/tcp.hpp

@@ -68,6 +68,8 @@ int tcp_read (fd_t s_, void *data_, size_t size_);
 
 void tcp_tune_loopback_fast_path (fd_t socket_);
 
+void tune_tcp_busy_poll (fd_t socket_, int busy_poll_);
+
 //  Resolves the given address_ string, opens a socket and sets socket options
 //  according to the passed options_. On success, returns the socket
 //  descriptor and assigns the resolved address to out_tcp_addr_. In case of

src/zmq_draft.h

@@ -69,6 +69,7 @@
 #define ZMQ_HELLO_MSG 110
 #define ZMQ_DISCONNECT_MSG 111
 #define ZMQ_PRIORITY 112
+#define ZMQ_BUSY_POLL 113
 
 /*  DRAFT ZMQ_RECONNECT_STOP options                                          */
 #define ZMQ_RECONNECT_STOP_CONN_REFUSED 0x1

tests/CMakeLists.txt

@@ -162,6 +162,9 @@ if(ENABLE_DRAFTS)
     test_hello_msg
     test_disconnect_msg
   )
+  if(ZMQ_HAVE_BUSY_POLL)
+    list(APPEND tests test_busy_poll)
+  endif()
 endif()
 
 if(ZMQ_HAVE_WS)

tests/test_busy_poll.cpp

@@ -0,0 +1,58 @@
+/*
+    Copyright (c) 2007-2021 Contributors as noted in the AUTHORS file
+
+    This file is part of libzmq, the ZeroMQ core engine in C++.
+
+    libzmq is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    As a special exception, the Contributors give you permission to link
+    this library with independent modules to produce an executable,
+    regardless of the license terms of these independent modules, and to
+    copy and distribute the resulting executable under terms of your choice,
+    provided that you also meet, for each linked independent module, the
+    terms and conditions of the license of that module. An independent
+    module is a module which is not derived from or based on this library.
+    If you modify this library, you must extend this exception to your
+    version of the library.
+
+    libzmq is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "testutil.hpp"
+#include "testutil_unity.hpp"
+
+SETUP_TEARDOWN_TESTCONTEXT
+
+void test_busy_poll ()
+{
+    //  Create a socket
+    void *socket = test_context_socket (ZMQ_DEALER);
+
+    //  set socket ZMQ_BUSY_POLL options
+    int busy_poll = 1;
+    TEST_ASSERT_SUCCESS_ERRNO (
+      zmq_setsockopt (socket, ZMQ_BUSY_POLL, &busy_poll, sizeof (int)));
+
+    //  bind socket
+    TEST_ASSERT_SUCCESS_ERRNO (zmq_bind (socket, "tcp://127.0.0.1:*"));
+
+    //  Clean up.
+    test_context_socket_close (socket);
+}
+
+int main ()
+{
+    setup_test_environment ();
+    UNITY_BEGIN ();
+    RUN_TEST (test_busy_poll);
+    return UNITY_END ();
+}