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cycles.h
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cycles.h
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/*
+----------------------------------------------------------------------+
| HipHop for PHP |
+----------------------------------------------------------------------+
| Copyright (c) 2010-present Facebook, Inc. (http://www.facebook.com) |
+----------------------------------------------------------------------+
| This source file is subject to version 3.01 of the PHP license, |
| that is bundled with this package in the file LICENSE, and is |
| available through the world-wide-web at the following url: |
| http://www.php.net/license/3_01.txt |
| If you did not receive a copy of the PHP license and are unable to |
| obtain it through the world-wide-web, please send a note to |
| license@php.net so we can mail you a copy immediately. |
+----------------------------------------------------------------------+
*/
#pragma once
#include <folly/portability/Asm.h>
#include "hphp/util/assertions.h"
namespace HPHP {
/*
* Return the underlying machine cycle counter. While this is slightly
* non-portable in theory, all the CPUs you're likely to care about support
* it in some way or another.
*/
inline uint64_t cpuCycles() {
#ifdef __x86_64__
uint64_t lo, hi;
asm volatile("rdtsc" : "=a"((lo)),"=d"(hi));
return lo | (hi << 32);
#elif __aarch64__
// FIXME: This returns the virtual timer which is not exactly
// the core cycles but has a different frequency.
uint64_t tb;
asm volatile("mrs %0, cntvct_el0" : "=r" (tb));
return tb;
#else
not_implemented();
#endif
}
inline void cpuRelax() {
folly::asm_volatile_pause();
}
inline void cycleDelay(uint32_t numCycles) {
auto start = cpuCycles();
do {
if (numCycles > 100) cpuRelax();
} while (cpuCycles() - start < numCycles);
}
}