zend_hrtime: use CLOCK_MONOTONIC instead of CLOCK_MONOTONIC_RAW (#23790)

CLOCK_MONOTONIC_RAW is not disciplined by NTP, so it ticks with the raw
frequency error of the underlying oscillator, which is 4% under WSL2 and
makes hrtime() disagree with microtime() by that much.

The slew that GH-19221 wanted to avoid is bounded to 500ppm by the kernel
and is what makes CLOCK_MONOTONIC track elapsed real time.

zend_hrtime_posix_clock_id stays for ABI compatibility, but nothing reads
it anymore.

Co-authored-by: Tim Düsterhus <tim@tideways-gmbh.com>

Author: nicolas-grekas

NEWS

@@ -26,6 +26,8 @@ PHP                                                                        NEWS
     constant, and as an alias in class_alias() and use declarations. (Girgias)
   . Deprecated using "_" as a constant name and as an alias for a class or
     constant in use declarations. (Girgias)
+  . Switch the POSIX high resolution timer back to CLOCK_MONOTONIC from
+    CLOCK_MONOTONIC_RAW. (nicolas-grekas)
 
 - FFI:
   . Fixed crashes with FFI callbacks created from __call() trampolines

Zend/zend_hrtime.c

@@ -70,19 +70,12 @@ void zend_startup_hrtime(void)
 
 	struct timespec ts;
 
-#ifdef CLOCK_MONOTONIC_RAW
-	if (EXPECTED(0 == clock_gettime(CLOCK_MONOTONIC_RAW, &ts))) {
-		zend_hrtime_posix_clock_id = CLOCK_MONOTONIC_RAW;
-		return;
-	}
-#endif
-
-	if (EXPECTED(0 == clock_gettime(zend_hrtime_posix_clock_id, &ts))) {
+	if (EXPECTED(0 == clock_gettime(CLOCK_MONOTONIC, &ts))) {
 		return;
 	}
 
 	// zend_error mechanism is not initialized at that point
-	fprintf(stderr, "No working CLOCK_MONOTONIC* found, this should never happen\n");
+	fprintf(stderr, "No working CLOCK_MONOTONIC found, this should never happen\n");
 	abort();
 
 #endif

Zend/zend_hrtime.h

@@ -72,6 +72,7 @@ ZEND_API extern mach_timebase_info_data_t zend_hrtime_timerlib_info;
 
 #elif ZEND_HRTIME_PLATFORM_POSIX
 
+/* Not read anymore, kept for ABI compatibility */
 ZEND_API extern clockid_t zend_hrtime_posix_clock_id;
 
 #endif
@@ -94,7 +95,7 @@ static zend_always_inline zend_hrtime_t zend_hrtime(void)
 	return (zend_hrtime_t)mach_absolute_time() * zend_hrtime_timerlib_info.numer / zend_hrtime_timerlib_info.denom;
 #elif ZEND_HRTIME_PLATFORM_POSIX
 	struct timespec ts = { .tv_sec = 0, .tv_nsec = 0 };
-	clock_gettime(zend_hrtime_posix_clock_id, &ts);
+	clock_gettime(CLOCK_MONOTONIC, &ts);
 	return ((zend_hrtime_t) ts.tv_sec * (zend_hrtime_t)ZEND_NANO_IN_SEC) + ts.tv_nsec;
 #elif ZEND_HRTIME_PLATFORM_HPUX
 	return (zend_hrtime_t) gethrtime();