[PATCH v2 1/1] ntdll: Don't use CLOCK_REALTIME_COARSE

[Tatsuyuki Ishi]

From: Tatsuyuki Ishi

This reverts commit 5c8ea25014f ("ntdll: Use CLOCK_REALTIME_COARSE for
NtQuerySystemTime() if it has sufficient resolution.")

CLOCK_*_COARSE only provides up to 1ms resolution at CONFIG_HZ=1000.
OTOH, there are several ways to get up to 0.5ms resolution on modern
Windows (high resolution waitable timers, NtSetTimerResolution with
0.5ms). This code path therefore has a possibility of behaving worse
than native.

Since COARSE resolution is HZ dependent, this code path only runs if the
kernel is configured with CONFIG_HZ=1000. Most distro ships does not
ship with this. Therefore, this code path is rarely tested, and is more
of a recipe for surprise. If any application rely on fast
NtQuerySystemTime they are likely already broken for majority of Wine
users.

Given the above reason, don't use CLOCK_REALTIME_COARSE. Use
gettimeofday which is internally hooked to CLOCK_REALTIME.
---
 dlls/ntdll/unix/sync.c | 31 +++----------------------------
 1 file changed, 3 insertions(+), 28 deletions(-)

diff --git a/dlls/ntdll/unix/sync.c b/dlls/ntdll/unix/sync.c
index bfbcaf4a851..97a6e2b5ffc 100644
--- a/dlls/ntdll/unix/sync.c
+++ b/dlls/ntdll/unix/sync.c
@@ -1579,35 +1579,10 @@ NTSTATUS WINAPI NtQueryPerformanceCounter( LARGE_INTEGER *counter, LARGE_INTEGER
  */
 NTSTATUS WINAPI NtQuerySystemTime( LARGE_INTEGER *time )
 {
-#ifdef HAVE_CLOCK_GETTIME
-    struct timespec ts;
-    static clockid_t clock_id = CLOCK_MONOTONIC; /* placeholder */
-
-    if (clock_id == CLOCK_MONOTONIC)
-    {
-#ifdef CLOCK_REALTIME_COARSE
-        struct timespec res;
-
-        /* Use CLOCK_REALTIME_COARSE if it has 1 ms or better resolution */
-        if (!clock_getres( CLOCK_REALTIME_COARSE, &res ) && res.tv_sec == 0 && res.tv_nsec <= 1000000)
-            clock_id = CLOCK_REALTIME_COARSE;
-        else
-#endif /* CLOCK_REALTIME_COARSE */
-            clock_id = CLOCK_REALTIME;
-    }
-
-    if (!clock_gettime( clock_id, &ts ))
-    {
-        time->QuadPart = ticks_from_time_t( ts.tv_sec ) + (ts.tv_nsec + 50) / 100;
-    }
-    else
-#endif /* HAVE_CLOCK_GETTIME */
-    {
-        struct timeval now;
+    struct timeval now;

-        gettimeofday( &now, 0 );
-        time->QuadPart = ticks_from_time_t( now.tv_sec ) + now.tv_usec * 10;
-    }
+    gettimeofday( &now, 0 );
+    time->QuadPart = ticks_from_time_t( now.tv_sec ) + now.tv_usec * 10;
     return STATUS_SUCCESS;
 }