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#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;
}
const char *monotonicInfoString() {
return monotonic_info_string;
}
monotonic_clock_type monotonicGetType() {
if (getMonotonicUs == getMonotonicUs_posix)
return MONOTONIC_CLOCK_POSIX;
return MONOTONIC_CLOCK_HW;
}
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