From 87b09d144ecbb5c9eea1bf604b9ec0d5a61875d0 Mon Sep 17 00:00:00 2001
From: Glenn Strauss <gstrauss@gluelogic.com>
Date: Mon, 12 Jul 2021 16:48:32 -0400
Subject: [PATCH] [core] use CLOCK_MONOTONIC_COARSE where available

server.c uses monotonic clock to detect change in second,
so CLOCK_MONOTONIC_COARSE clock resolution (often ~1ms)
is more than sufficient.  (Obtaining CLOCK_MONOTONIC_COARSE
can be faster than CLOCK_MONOTONIC.)

reference:
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux_for_real_time/7/html/reference_guide/sect-posix_clocks
---
 src/log.c    | 26 +++++++-------------------
 src/log.h    |  2 +-
 src/server.c | 24 +++++++++++++++++++++++-
 3 files changed, 31 insertions(+), 21 deletions(-)

diff --git a/src/log.c b/src/log.c
index 75176f08..0fbf352b 100644
--- a/src/log.c
+++ b/src/log.c
@@ -24,13 +24,13 @@
 unix_time64_t log_epoch_secs = 0;
 unix_time64_t log_monotonic_secs = 0;
 
-int log_clock_gettime_realtime (unix_timespec64_t *ts) {
+int log_clock_gettime (const int clockid, unix_timespec64_t * const ts) {
   #ifdef HAVE_CLOCK_GETTIME
    #if HAS_TIME_BITS64
-    return clock_gettime(CLOCK_REALTIME, ts);
+    return clock_gettime(clockid, ts);
    #else
     struct timespec ts32;
-    int rc = clock_gettime(CLOCK_REALTIME, &ts32);
+    int rc = clock_gettime(clockid, &ts32);
     if (0 == rc) {
         /*(treat negative 32-bit tv.tv_sec as unsigned)*/
         ts->tv_sec  = TIME64_CAST(ts32.tv_sec);
@@ -44,6 +44,7 @@ int log_clock_gettime_realtime (unix_timespec64_t *ts) {
      *      && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200 */
     struct timeval tv;
     gettimeofday(&tv, NULL);
+    UNUSED(clockid);
    #if HAS_TIME_BITS64
     ts->tv_sec = tv.tv_sec;
    #else /*(treat negative 32-bit tv.tv_sec as unsigned)*/
@@ -54,24 +55,11 @@ int log_clock_gettime_realtime (unix_timespec64_t *ts) {
   #endif
 }
 
-int log_clock_gettime_monotonic (unix_timespec64_t *ts) {
+int log_clock_gettime_realtime (unix_timespec64_t *ts) {
   #ifdef HAVE_CLOCK_GETTIME
-   #if HAS_TIME_BITS64
-    return clock_gettime(CLOCK_MONOTONIC, ts);
-   #else
-    struct timespec ts32;
-    int rc = clock_gettime(CLOCK_MONOTONIC, &ts32);
-    if (0 == rc) {
-        /*(treat negative 32-bit tv.tv_sec as unsigned)*/
-        /*(negative 32-bit should not happen on monotonic clock
-         * unless system running continously for > 68 years)*/
-        ts->tv_sec  = TIME64_CAST(ts32.tv_sec);
-        ts->tv_nsec = ts32.tv_nsec;
-    }
-    return rc;
-   #endif
+    return log_clock_gettime(CLOCK_REALTIME, ts);
   #else
-    return log_clock_gettime_realtime(ts); /*(fallback)*/
+    return log_clock_gettime(0, ts);
   #endif
 }
 
diff --git a/src/log.h b/src/log.h
index 4a4d9bbf..6d3e1aee 100644
--- a/src/log.h
+++ b/src/log.h
@@ -8,8 +8,8 @@
 extern unix_time64_t log_epoch_secs;
 extern unix_time64_t log_monotonic_secs;
 
+int log_clock_gettime(int clockid, unix_timespec64_t *ts);
 int log_clock_gettime_realtime (unix_timespec64_t *ts);
-int log_clock_gettime_monotonic (unix_timespec64_t *ts);
 
 ssize_t write_all(int fd, const void* buf, size_t count);
 
diff --git a/src/server.c b/src/server.c
index ed9efb31..80a57d4b 100644
--- a/src/server.c
+++ b/src/server.c
@@ -222,11 +222,13 @@ static int daemonize(void) {
 }
 #endif
 
+static int clockid_mono_coarse = 0;
+
 static unix_time64_t
 server_monotonic_secs (void)
 {
     unix_timespec64_t ts;
-    return (0 == log_clock_gettime_monotonic(&ts))
+    return (0 == log_clock_gettime(clockid_mono_coarse, &ts))
       ? ts.tv_sec
       : log_monotonic_secs;
 }
@@ -272,6 +274,26 @@ static server *server_init(void) {
 	li_rand_reseed();
 
 	srv->startup_ts = log_epoch_secs = TIME64_CAST(time(NULL));
+  #ifdef HAVE_CLOCK_GETTIME
+	unix_timespec64_t ts;
+	UNUSED(&ts);
+   #ifdef CLOCK_MONOTONIC_COARSE
+	if (0 == log_clock_gettime(CLOCK_MONOTONIC_COARSE, &ts))
+		clockid_mono_coarse = CLOCK_MONOTONIC_COARSE;
+	else
+   #endif
+   #ifdef CLOCK_MONOTONIC_RAW_APPROX
+	if (0 == log_clock_gettime(CLOCK_MONOTONIC_RAW_APPROX, &ts))
+		clockid_mono_coarse = CLOCK_MONOTONIC_RAW_APPROX;
+	else
+   #endif
+   #ifdef CLOCK_MONOTONIC_RAW
+	if (0 == log_clock_gettime(CLOCK_MONOTONIC_RAW, &ts))
+		clockid_mono_coarse = CLOCK_MONOTONIC_RAW;
+	else
+   #endif
+		clockid_mono_coarse = CLOCK_MONOTONIC;
+  #endif
 	log_monotonic_secs = server_monotonic_secs();
 
 	srv->errh = log_error_st_init();