rmonotonic: a monotonic clock source

deps/CMakeLists.txt

@@ -9,6 +9,7 @@ ADD_SUBDIRECTORY(lz4)
 ADD_SUBDIRECTORY(cJson)
 ADD_SUBDIRECTORY(wepoll)
 ADD_SUBDIRECTORY(MsvcLibX)
+ADD_SUBDIRECTORY(rmonotonic)
 
 IF (TD_LINUX AND TD_MQTT)
   ADD_SUBDIRECTORY(MQTT-C)

deps/rmonotonic/CMakeLists.txt

+AUX_SOURCE_DIRECTORY(${CMAKE_CURRENT_SOURCE_DIR}/src SOURCE_LIST)
+
+add_definitions(-DUSE_PROCESSOR_CLOCK)
+
+ADD_LIBRARY(rmonotonic ${SOURCE_LIST})
+TARGET_INCLUDE_DIRECTORIES(rmonotonic PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/inc)

deps/rmonotonic/inc/monotonic.h

+#ifndef __MONOTONIC_H
+#define __MONOTONIC_H
+/* The monotonic clock is an always increasing clock source.  It is unrelated to
+ * the actual time of day and should only be used for relative timings.  The
+ * monotonic clock is also not guaranteed to be chronologically precise; there
+ * may be slight skew/shift from a precise clock.
+ *
+ * Depending on system architecture, the monotonic time may be able to be
+ * retrieved much faster than a normal clock source by using an instruction
+ * counter on the CPU.  On x86 architectures (for example), the RDTSC
+ * instruction is a very fast clock source for this purpose.
+ */
+
+//#include "fmacros.h"
+#include <stdint.h>
+//#include <unistd.h>
+
+/* A counter in micro-seconds.  The 'monotime' type is provided for variables
+ * holding a monotonic time.  This will help distinguish & document that the
+ * variable is associated with the monotonic clock and should not be confused
+ * with other types of time.*/
+typedef uint64_t monotime;
+
+/* Retrieve counter of micro-seconds relative to an arbitrary point in time.  */
+extern monotime (*getMonotonicUs)(void);
+
+
+/* Call once at startup to initialize the monotonic clock.  Though this only
+ * needs to be called once, it may be called additional times without impact.
+ * Returns a printable string indicating the type of clock initialized.
+ * (The returned string is static and doesn't need to be freed.)  */
+const char * monotonicInit();
+
+
+/* Functions to measure elapsed time.  Example:
+ *     monotime myTimer;
+ *     elapsedStart(&myTimer);
+ *     while (elapsedMs(myTimer) < 10) {} // loops for 10ms
+ */
+static inline void elapsedStart(monotime *start_time) {
+    *start_time = getMonotonicUs();
+}
+
+static inline uint64_t elapsedUs(monotime start_time) {
+    return getMonotonicUs() - start_time;
+}
+
+static inline uint64_t elapsedMs(monotime start_time) {
+    return elapsedUs(start_time) / 1000;
+}
+
+#endif

deps/rmonotonic/src/monotonic.c

+#include "monotonic.h"
+#include <stddef.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <time.h>
+
+#undef NDEBUG
+#include <assert.h>
+
+
+/* The function pointer for clock retrieval.  */
+monotime (*getMonotonicUs)(void) = NULL;
+
+static char monotonic_info_string[32];
+
+
+/* Using the processor clock (aka TSC on x86) can provide improved performance
+ * throughout Redis wherever the monotonic clock is used.  The processor clock
+ * is significantly faster than calling 'clock_getting' (POSIX).  While this is
+ * generally safe on modern systems, this link provides additional information
+ * about use of the x86 TSC: http://oliveryang.net/2015/09/pitfalls-of-TSC-usage
+ *
+ * To use the processor clock, either uncomment this line, or build with
+ *   CFLAGS="-DUSE_PROCESSOR_CLOCK"
+#define USE_PROCESSOR_CLOCK
+ */
+
+
+#if defined(USE_PROCESSOR_CLOCK) && defined(__x86_64__) && defined(__linux__)
+#include <regex.h>
+#include <x86intrin.h>
+
+static long mono_ticksPerMicrosecond = 0;
+
+static monotime getMonotonicUs_x86() {
+    return __rdtsc() / mono_ticksPerMicrosecond;
+}
+
+static void monotonicInit_x86linux() {
+    const int bufflen = 256;
+    char buf[bufflen];
+    regex_t cpuGhzRegex, constTscRegex;
+    const size_t nmatch = 2;
+    regmatch_t pmatch[nmatch];
+    int constantTsc = 0;
+    int rc;
+
+    /* Determine the number of TSC ticks in a micro-second.  This is
+     * a constant value matching the standard speed of the processor.
+     * On modern processors, this speed remains constant even though
+     * the actual clock speed varies dynamically for each core.  */
+    rc = regcomp(&cpuGhzRegex, "^model name\\s+:.*@ ([0-9.]+)GHz", REG_EXTENDED);
+    assert(rc == 0);
+
+    /* Also check that the constant_tsc flag is present.  (It should be
+     * unless this is a really old CPU.  */
+    rc = regcomp(&constTscRegex, "^flags\\s+:.* constant_tsc", REG_EXTENDED);
+    assert(rc == 0);
+
+    FILE *cpuinfo = fopen("/proc/cpuinfo", "r");
+    if (cpuinfo != NULL) {
+        while (fgets(buf, bufflen, cpuinfo) != NULL) {
+            if (regexec(&cpuGhzRegex, buf, nmatch, pmatch, 0) == 0) {
+                buf[pmatch[1].rm_eo] = '\0';
+                double ghz = atof(&buf[pmatch[1].rm_so]);
+                mono_ticksPerMicrosecond = (long)(ghz * 1000);
+                break;
+            }
+        }
+        while (fgets(buf, bufflen, cpuinfo) != NULL) {
+            if (regexec(&constTscRegex, buf, nmatch, pmatch, 0) == 0) {
+                constantTsc = 1;
+                break;
+            }
+        }
+
+        fclose(cpuinfo);
+    }
+    regfree(&cpuGhzRegex);
+    regfree(&constTscRegex);
+
+    if (mono_ticksPerMicrosecond == 0) {
+        fprintf(stderr, "monotonic: x86 linux, unable to determine clock rate");
+        return;
+    }
+    if (!constantTsc) {
+        fprintf(stderr, "monotonic: x86 linux, 'constant_tsc' flag not present");
+        return;
+    }
+
+    snprintf(monotonic_info_string, sizeof(monotonic_info_string),
+            "X86 TSC @ %ld ticks/us", mono_ticksPerMicrosecond);
+    getMonotonicUs = getMonotonicUs_x86;
+}
+#endif
+
+
+#if defined(USE_PROCESSOR_CLOCK) && defined(__aarch64__)
+static long mono_ticksPerMicrosecond = 0;
+
+/* Read the clock value.  */
+static inline uint64_t __cntvct() {
+    uint64_t virtual_timer_value;
+    __asm__ volatile("mrs %0, cntvct_el0" : "=r"(virtual_timer_value));
+    return virtual_timer_value;
+}
+
+/* Read the Count-timer Frequency.  */
+static inline uint32_t cntfrq_hz() {
+    uint64_t virtual_freq_value;
+    __asm__ volatile("mrs %0, cntfrq_el0" : "=r"(virtual_freq_value));
+    return (uint32_t)virtual_freq_value;    /* top 32 bits are reserved */
+}
+
+static monotime getMonotonicUs_aarch64() {
+    return __cntvct() / mono_ticksPerMicrosecond;
+}
+
+static void monotonicInit_aarch64() {
+    mono_ticksPerMicrosecond = (long)cntfrq_hz() / 1000L / 1000L;
+    if (mono_ticksPerMicrosecond == 0) {
+        fprintf(stderr, "monotonic: aarch64, unable to determine clock rate");
+        return;
+    }
+
+    snprintf(monotonic_info_string, sizeof(monotonic_info_string),
+            "ARM CNTVCT @ %ld ticks/us", mono_ticksPerMicrosecond);
+    getMonotonicUs = getMonotonicUs_aarch64;
+}
+#endif
+
+
+static monotime getMonotonicUs_posix() {
+    /* clock_gettime() is specified in POSIX.1b (1993).  Even so, some systems
+     * did not support this until much later.  CLOCK_MONOTONIC is technically
+     * optional and may not be supported - but it appears to be universal.
+     * If this is not supported, provide a system-specific alternate version.  */
+    struct timespec ts;
+    clock_gettime(CLOCK_MONOTONIC, &ts);
+    return ((uint64_t)ts.tv_sec) * 1000000 + ts.tv_nsec / 1000;
+}
+
+static void monotonicInit_posix() {
+    /* Ensure that CLOCK_MONOTONIC is supported.  This should be supported
+     * on any reasonably current OS.  If the assertion below fails, provide
+     * an appropriate alternate implementation.  */
+    struct timespec ts;
+    int rc = clock_gettime(CLOCK_MONOTONIC, &ts);
+    assert(rc == 0);
+
+    snprintf(monotonic_info_string, sizeof(monotonic_info_string),
+            "POSIX clock_gettime");
+    getMonotonicUs = getMonotonicUs_posix;
+}
+
+
+
+const char * monotonicInit() {
+    #if defined(USE_PROCESSOR_CLOCK) && defined(__x86_64__) && defined(__linux__)
+    if (getMonotonicUs == NULL) monotonicInit_x86linux();
+    #endif
+
+    #if defined(USE_PROCESSOR_CLOCK) && defined(__aarch64__)
+    if (getMonotonicUs == NULL) monotonicInit_aarch64();
+    #endif
+
+    if (getMonotonicUs == NULL) monotonicInit_posix();
+
+    return monotonic_info_string;
+}