From: Brandon Paupore <brandon.paupore@wdc.com>
Date: Tue, 12 Oct 2021 19:00:41 +0000 (-0500)
Subject: Query Windows clock frequency and use reported max
X-Git-Tag: fio-3.29~69^2
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=3d0d549ab34f64d19a4ee0a0ffdd4f79ebba48ec;p=fio.git

Query Windows clock frequency and use reported max

Previously FIO used the Windows lower-bound clock frequency of 64 Hz for
its helper-thread. This caused IOPS/BW logs to have large drift between
timestamps when not using per-unit logging for those measurements.

Now query the current resolution and set to use the maximum for more
accurate timestamps. Note that the resolution is automatically restored
after FIO terminates.

Signed-off-by: Brandon Paupore <brandon.paupore@wdc.com>
---

diff --git a/Makefile b/Makefile
index 5198f70e..c3feb53f 100644
--- a/Makefile
+++ b/Makefile
@@ -275,8 +275,8 @@ ifeq ($(CONFIG_TARGET_OS), Darwin)
   LIBS	 += -lpthread -ldl
 endif
 ifneq (,$(findstring CYGWIN,$(CONFIG_TARGET_OS)))
-  SOURCE += os/windows/cpu-affinity.c os/windows/posix.c
-  WINDOWS_OBJS = os/windows/cpu-affinity.o os/windows/posix.o lib/hweight.o
+  SOURCE += os/windows/cpu-affinity.c os/windows/posix.c os/windows/dlls.c
+  WINDOWS_OBJS = os/windows/cpu-affinity.o os/windows/posix.o os/windows/dlls.o lib/hweight.o
   LIBS	 += -lpthread -lpsapi -lws2_32 -lssp
   FIO_CFLAGS += -DPSAPI_VERSION=1 -Ios/windows/posix/include -Wno-format
 endif
diff --git a/helper_thread.c b/helper_thread.c
index d8e7ebfe..b9b83db3 100644
--- a/helper_thread.c
+++ b/helper_thread.c
@@ -9,6 +9,10 @@
 #define DRD_IGNORE_VAR(x) do { } while (0)
 #endif
 
+#ifdef WIN32
+#include "os/os-windows.h"
+#endif
+
 #include "fio.h"
 #include "smalloc.h"
 #include "helper_thread.h"
@@ -283,19 +287,12 @@ static void *helper_thread_main(void *data)
 		}
 	};
 	struct timespec ts;
-	int clk_tck, ret = 0;
+	long clk_tck;
+	int ret = 0;
 
-#ifdef _SC_CLK_TCK
-	clk_tck = sysconf(_SC_CLK_TCK);
-#else
-	/*
-	 * The timer frequence is variable on Windows. Instead of trying to
-	 * query it, use 64 Hz, the clock frequency lower bound. See also
-	 * https://carpediemsystems.co.uk/2019/07/18/windows-system-timer-granularity/.
-	 */
-	clk_tck = 64;
-#endif
-	dprint(FD_HELPERTHREAD, "clk_tck = %d\n", clk_tck);
+	os_clk_tck(&clk_tck);
+
+	dprint(FD_HELPERTHREAD, "clk_tck = %ld\n", clk_tck);
 	assert(clk_tck > 0);
 	sleep_accuracy_ms = (1000 + clk_tck - 1) / clk_tck;
 
diff --git a/os/os.h b/os/os.h
index 827b61e9..5965d7b8 100644
--- a/os/os.h
+++ b/os/os.h
@@ -412,4 +412,13 @@ static inline bool os_cpu_has(cpu_features feature)
 # define fio_mkdir(path, mode)	mkdir(path, mode)
 #endif
 
+#ifdef _SC_CLK_TCK
+static inline void os_clk_tck(long *clk_tck)
+{
+	*clk_tck = sysconf(_SC_CLK_TCK);
+}
+#else
+extern void os_clk_tck(long *clk_tck);
+#endif
+
 #endif /* FIO_OS_H */
diff --git a/os/windows/dlls.c b/os/windows/dlls.c
new file mode 100644
index 00000000..774b1c61
--- /dev/null
+++ b/os/windows/dlls.c
@@ -0,0 +1,33 @@
+#include "os/os.h"
+
+#include <windows.h>
+
+void os_clk_tck(long *clk_tck)
+{
+	/*
+	 * The timer resolution is variable on Windows. Try to query it 
+	 * or use 64 Hz, the clock frequency lower bound. See also
+	 * https://carpediemsystems.co.uk/2019/07/18/windows-system-timer-granularity/.
+	 */
+	unsigned long minRes, maxRes, curRes;
+	HMODULE lib;
+	FARPROC queryTimer;
+	FARPROC setTimer;
+
+	if (!(lib = LoadLibrary(TEXT("ntdll.dll"))) ||
+		!(queryTimer = GetProcAddress(lib, "NtQueryTimerResolution")) ||
+		!(setTimer = GetProcAddress(lib, "NtSetTimerResolution"))) {
+		dprint(FD_HELPERTHREAD, 
+			"Failed to load ntdll library, set to lower bound 64 Hz\n");
+		*clk_tck = 64;
+	} else {
+		queryTimer(&minRes, &maxRes, &curRes);
+		dprint(FD_HELPERTHREAD, 
+			"minRes = %lu, maxRes = %lu, curRes = %lu\n",
+			minRes, maxRes, curRes);
+
+		/* Use maximum resolution for most accurate timestamps */
+		setTimer(maxRes, 1, &curRes);
+		*clk_tck = (long) (10000000L / maxRes);
+	}
+}
\ No newline at end of file
diff --git a/stat.c b/stat.c
index ac53463d..30f9b5c1 100644
--- a/stat.c
+++ b/stat.c
@@ -17,7 +17,11 @@
 #include "zbd.h"
 #include "oslib/asprintf.h"
 
+#ifdef WIN32
+#define LOG_MSEC_SLACK	2
+#else
 #define LOG_MSEC_SLACK	1
+#endif
 
 struct fio_sem *stat_sem;