clock_t class added

src/Makefile.am

@@ -54,6 +54,7 @@ libzmq_la_SOURCES = \
     atomic_counter.hpp \
     atomic_ptr.hpp \
     blob.hpp \
+    clock.hpp \
     command.hpp \
     config.hpp \
     connect_session.hpp \
@@ -121,6 +122,7 @@ libzmq_la_SOURCES = \
     zmq_engine.hpp \
     zmq_init.hpp \
     zmq_listener.hpp \
+    clock.cpp \
     command.cpp \
     ctx.cpp \
     connect_session.cpp \

src/clock.cpp

@@ -0,0 +1,100 @@
+/*
+    Copyright (c) 2007-2010 iMatix Corporation
+
+    This file is part of 0MQ.
+
+    0MQ is free software; you can redistribute it and/or modify it under
+    the terms of the Lesser GNU General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    0MQ 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
+    Lesser GNU General Public License for more details.
+
+    You should have received a copy of the Lesser GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "clock.hpp"
+#include "platform.hpp"
+#include "likely.hpp"
+#include "config.hpp"
+#include "err.hpp"
+
+#include <stddef.h>
+
+#if !defined ZMQ_HAVE_WINDOWS
+#include <sys/time.h>
+#endif
+
+zmq::clock_t::clock_t () :
+    last_tsc (rdtsc ()),
+    last_time (now_us ())
+{
+}
+
+zmq::clock_t::~clock_t ()
+{
+}
+
+uint64_t zmq::clock_t::now_us ()
+{
+#if defined ZMQ_HAVE_WINDOWS
+
+    //  Get the high resolution counter's accuracy.
+    LARGE_INTEGER ticksPerSecond;
+    QueryPerformanceFrequency (&ticksPerSecond);
+
+    //  What time is it?
+    LARGE_INTEGER tick;
+    QueryPerformanceCounter (&tick);
+
+    //  Convert the tick number into the number of seconds
+    //  since the system was started.
+    double ticks_div = (double) (ticksPerSecond.QuadPart / 1000000);     
+    return (uint64_t) (tick.QuadPart / ticks_div);
+
+#else
+
+    //  Use POSIX gettimeofday function to get precise time.
+    struct timeval tv;
+    int rc = gettimeofday (&tv, NULL);
+    errno_assert (rc == 0);
+    return (tv.tv_sec * (uint64_t) 1000000 + tv.tv_usec);
+
+#endif
+}
+
+uint64_t zmq::clock_t::now_ms ()
+{
+    uint64_t tsc = rdtsc ();
+
+    //  If TSC is not supported, get precise time and chop off the microseconds.
+    if (!tsc)
+        return now_us () / 1000;
+
+    //  If TSC haven't jumped back (in case of migration to a different
+    //  CPU core) and if not too much time elapsed since last measurement,
+    //  we can return cached time value.
+    if (likely (tsc - last_tsc <= (clock_precision / 2) && tsc >= last_tsc))
+        return last_time;
+
+    last_tsc = tsc;
+    last_time = now_us ();
+    return last_time;
+}
+
+uint64_t zmq::clock_t::rdtsc ()
+{
+#if (defined _MSC_VER && (defined _M_IX86 || defined _M_X64))
+    uint64_t current_time = __rdtsc ();
+#elif (defined __GNUC__ && (defined __i386__ || defined __x86_64__))
+    uint32_t low, high;
+    __asm__ volatile ("rdtsc" : "=a" (low), "=d" (high));
+    return (uint64_t) high << 32 | low;
+#else
+    return 0;
+#endif
+}

src/clock.hpp

@@ -0,0 +1,56 @@
+/*
+    Copyright (c) 2007-2010 iMatix Corporation
+
+    This file is part of 0MQ.
+
+    0MQ is free software; you can redistribute it and/or modify it under
+    the terms of the Lesser GNU General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    0MQ 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
+    Lesser GNU General Public License for more details.
+
+    You should have received a copy of the Lesser GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __ZMQ_CLOCK_HPP_INCLUDED__
+#define __ZMQ_CLOCK_HPP_INCLUDED__
+
+#include "stdint.hpp"
+
+namespace zmq
+{
+
+    class clock_t
+    {
+    public:
+
+        clock_t ();
+        ~clock_t ();
+
+        //  CPU's timestamp counter. Returns 0 if it's not available.
+        static uint64_t rdtsc ();
+
+        //  High precision timestamp.
+        static uint64_t now_us ();
+
+        //  Low precision timestamp. In tight loops generating it can be
+        //  10 to 100 times faster than the high precision timestamp.
+        uint64_t now_ms ();
+
+    private:
+
+        uint64_t last_tsc;
+        uint64_t last_time;
+
+        clock_t (const clock_t&);
+        void operator = (const clock_t&);
+    };
+
+}
+
+#endif

src/config.hpp

@@ -76,6 +76,13 @@ namespace zmq
         //  3,000,000 ticks equals to 1 - 2 milliseconds on current CPUs.
         max_command_delay = 3000000,
 
+        //  Low-precision clock precision in CPU ticks. 1ms. Value of 1000000
+        //  should be OK for CPU frequencies above 1GHz. If should work
+        //  reasonably well fro CPU frequencies above 500MHz. For lower CPU
+        //  frequencies you may consider lowering this value to get best
+        //  possible latencies.
+        clock_precision = 1000000,
+
         //  Maximal number of non-accepted connections that can be held by
         //  TCP listener object.
         tcp_connection_backlog = 10,

src/socket_base.cpp

@@ -40,6 +40,7 @@
 #include "io_thread.hpp"
 #include "connect_session.hpp"
 #include "config.hpp"
+#include "clock.hpp"
 #include "pipe.hpp"
 #include "err.hpp"
 #include "ctx.hpp"
@@ -56,14 +57,6 @@
 #include "xrep.hpp"
 #include "uuid.hpp"
 
-//  If the RDTSC is available we use it to prevent excessive
-//  polling for commands. The nice thing here is that it will work on any
-//  system with x86 architecture and gcc or MSVC compiler.
-#if (defined __GNUC__ && (defined __i386__ || defined __x86_64__)) ||\
-    (defined _MSC_VER && (defined _M_IX86 || defined _M_X64))
-#define ZMQ_DELAY_COMMANDS
-#endif
-
 zmq::socket_base_t *zmq::socket_base_t::create (int type_, class ctx_t *parent_,
     uint32_t slot_)
 {
@@ -109,7 +102,7 @@ zmq::socket_base_t::socket_base_t (ctx_t *parent_, uint32_t slot_) :
     own_t (parent_, slot_),
     ctx_terminated (false),
     destroyed (false),
-    last_processing_time (0),
+    last_tsc (0),
     ticks (0),
     rcvmore (false)
 {
@@ -486,7 +479,7 @@ int zmq::socket_base_t::recv (::zmq_msg_t *msg_, int flags_)
     //
     //  Note that 'recv' uses different command throttling algorithm (the one
     //  described above) from the one used by 'send'. This is because counting
-    //  ticks is more efficient than doing rdtsc all the time.
+    //  ticks is more efficient than doing RDTSC all the time.
     if (++ticks == inbound_poll_rate) {
         if (unlikely (process_commands (false, false) != 0))
             return -1;
@@ -627,35 +620,24 @@ int zmq::socket_base_t::process_commands (bool block_, bool throttle_)
     }
     else {
 
-#if defined ZMQ_DELAY_COMMANDS
+        //  Get the CPU's tick counter. If 0, the counter is not available.
+        uint64_t tsc = zmq::clock_t::rdtsc ();
+
         //  Optimised version of command processing - it doesn't have to check
         //  for incoming commands each time. It does so only if certain time
         //  elapsed since last command processing. Command delay varies
         //  depending on CPU speed: It's ~1ms on 3GHz CPU, ~2ms on 1.5GHz CPU
         //  etc. The optimisation makes sense only on platforms where getting
         //  a timestamp is a very cheap operation (tens of nanoseconds).
-        if (throttle_) {
+        if (tsc && throttle_) {
 
-            //  Get timestamp counter.
-#if defined __GNUC__
-            uint32_t low;
-            uint32_t high;
-            __asm__ volatile ("rdtsc" : "=a" (low), "=d" (high));
-            uint64_t current_time = (uint64_t) high << 32 | low;
-#elif defined _MSC_VER
-            uint64_t current_time = __rdtsc ();
-#else
-#error
-#endif
             //  Check whether TSC haven't jumped backwards (in case of migration
             //  between CPU cores) and whether certain time have elapsed since
             //  last command processing. If it didn't do nothing.
-            if (current_time >= last_processing_time &&
-                  current_time - last_processing_time <= max_command_delay)
+            if (tsc >= last_tsc && tsc - last_tsc <= max_command_delay)
                 return 0;
-            last_processing_time = current_time;
+            last_tsc = tsc;
         }
-#endif
 
         //  Check whether there are any commands pending for this thread.
         rc = signaler.recv (&cmd, false);

src/socket_base.hpp

@@ -156,7 +156,7 @@ namespace zmq
         signaler_t signaler;
 
         //  Timestamp of when commands were processed the last time.
-        uint64_t last_processing_time;
+        uint64_t last_tsc;
 
         //  Number of messages received since last command processing.
         int ticks;

src/zmq.cpp

@@ -33,6 +33,7 @@
 #include "platform.hpp"
 #include "stdint.hpp"
 #include "config.hpp"
+#include "clock.hpp"
 #include "ctx.hpp"
 #include "err.hpp"
 #include "fd.hpp"
@@ -47,7 +48,6 @@
 
 #if !defined ZMQ_HAVE_WINDOWS
 #include <unistd.h>
-#include <sys/time.h>
 #endif
 
 #if defined ZMQ_HAVE_OPENPGM
@@ -660,59 +660,26 @@ int zmq_device (int device_, void *insocket_, void *outsocket_)
 //  0MQ utils - to be used by perf tests
 ////////////////////////////////////////////////////////////////////////////////
 
+void zmq_sleep (int seconds_)
+{
 #if defined ZMQ_HAVE_WINDOWS
-
-static uint64_t now ()
-{    
-    //  Get the high resolution counter's accuracy.
-    LARGE_INTEGER ticksPerSecond;
-    QueryPerformanceFrequency (&ticksPerSecond);
-
-    //  What time is it?
-    LARGE_INTEGER tick;
-    QueryPerformanceCounter (&tick);
-
-    //  Convert the tick number into the number of seconds
-    //  since the system was started.
-    double ticks_div = (double) (ticksPerSecond.QuadPart / 1000000);     
-    return (uint64_t) (tick.QuadPart / ticks_div);
-}
-
-void zmq_sleep (int seconds_)
-{
     Sleep (seconds_ * 1000);
-}
-
 #else
-
-static uint64_t now ()
-{
-    struct timeval tv;
-    int rc;
-
-    rc = gettimeofday (&tv, NULL);
-    assert (rc == 0);
-    return (tv.tv_sec * (uint64_t) 1000000 + tv.tv_usec);
-}
-
-void zmq_sleep (int seconds_)
-{
     sleep (seconds_);
-}
-
 #endif
+}
 
 void *zmq_stopwatch_start ()
 {
     uint64_t *watch = (uint64_t*) malloc (sizeof (uint64_t));
     assert (watch);
-    *watch = now ();
+    *watch = zmq::clock_t::now_us ();
     return (void*) watch;
 }
 
 unsigned long zmq_stopwatch_stop (void *watch_)
 {
-    uint64_t end = now ();
+    uint64_t end = zmq::clock_t::now_us ();
     uint64_t start = *(uint64_t*) watch_;
     free (watch_);
     return (unsigned long) (end - start);