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vm: add a comment on possible issues with QueryPerformanceCounter

char-rename
Alexander Iljin 2016-07-25 02:02:40 +03:00 committed by John Benediktsson
parent acd22d1218
commit 56880fbacf
1 changed files with 6 additions and 0 deletions
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6
vm/os-windows.cpp
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@ -151,6 +151,12 @@ uint64_t nano_count() {
static uint32_t hi = 0; static uint32_t hi = 0;
static uint32_t lo = 0; static uint32_t lo = 0;
// Note: on older systems QueryPerformanceCounter may be unreliable
// until you add /usepmtimer to Boot.ini. I had an issue where two
// nano_count calls would show a difference of about 1 second,
// while actually about 80 seconds have passed. The /usepmtimer
// switch cured the issue on that PC (WinXP Pro SP3 32-bit).
// See also http://www.virtualdub.org/blog/pivot/entry.php?id=106
LARGE_INTEGER count; LARGE_INTEGER count;
BOOL ret = QueryPerformanceCounter(&count); BOOL ret = QueryPerformanceCounter(&count);
if (ret == 0) if (ret == 0)