ref: ba4dc85441476d87b83d103a5ae646ce2903686c
parent: 1cb039529d4c1b535093c759850835fae794d424
parent: a81768561ca1de2a947a45f224bf91d3913c1e2a
author: Elliott Karpilovsky <elliottk@google.com>
date: Fri Dec 21 16:31:49 EST 2018
Merge "Improve accuracy of benchmarking"
--- a/vpx_ports/x86.h
+++ b/vpx_ports/x86.h
@@ -223,11 +223,26 @@
return flags & mask;
}
-// Note:
-// 32-bit CPU cycle counter is light-weighted for most function performance
-// measurement. For large function (CPU time > a couple of seconds), 64-bit
-// counter should be used.
-// 32-bit CPU cycle counter
+// Fine-Grain Measurement Functions
+//
+// If you are timing a small region of code, access the timestamp counter
+// (TSC) via:
+//
+// unsigned int start = x86_tsc_start();
+// ...
+// unsigned int end = x86_tsc_end();
+// unsigned int diff = end - start;
+//
+// The start/end functions introduce a few more instructions than using
+// x86_readtsc directly, but prevent the CPU's out-of-order execution from
+// affecting the measurement (by having earlier/later instructions be evaluated
+// in the time interval). See the white paper, "How to Benchmark Code
+// Execution Times on Intel® IA-32 and IA-64 Instruction Set Architectures" by
+// Gabriele Paoloni for more information.
+//
+// If you are timing a large function (CPU time > a couple of seconds), use
+// x86_readtsc64 to read the timestamp counter in a 64-bit integer. The
+// out-of-order leakage that can occur is minimal compared to total runtime.
static INLINE unsigned int x86_readtsc(void) {#if defined(__GNUC__) && __GNUC__
unsigned int tsc;
@@ -262,6 +277,41 @@
__asm rdtsc;
#endif
#endif
+}
+
+// 32-bit CPU cycle counter with a partial fence against out-of-order execution.
+static INLINE unsigned int x86_readtscp(void) {+#if defined(__GNUC__) && __GNUC__
+ unsigned int tscp;
+ __asm__ __volatile__("rdtscp\n\t" : "=a"(tscp) :);+ return tscp;
+#elif defined(__SUNPRO_C) || defined(__SUNPRO_CC)
+ unsigned int tscp;
+ asm volatile("rdtscp\n\t" : "=a"(tscp) :);+ return tscp;
+#elif defined(_MSC_VER)
+ unsigned int ui;
+ return (unsigned int)__rdtscp(&ui);
+#else
+#if ARCH_X86_64
+ return (unsigned int)__rdtscp();
+#else
+ __asm rdtscp;
+#endif
+#endif
+}
+
+static INLINE unsigned int x86_tsc_start(void) {+ unsigned int reg_eax, reg_ebx, reg_ecx, reg_edx;
+ cpuid(0, 0, reg_eax, reg_ebx, reg_ecx, reg_edx);
+ return x86_readtsc();
+}
+
+static INLINE unsigned int x86_tsc_end(void) {+ uint32_t v = x86_readtscp();
+ unsigned int reg_eax, reg_ebx, reg_ecx, reg_edx;
+ cpuid(0, 0, reg_eax, reg_ebx, reg_ecx, reg_edx);
+ return v;
}
#if defined(__GNUC__) && __GNUC__