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EDIT :: my_cpu.h
#ifndef MY_CPU_INCLUDED #define MY_CPU_INCLUDED /* Copyright (c) 2013, 2020, MariaDB This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; version 2 of the License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */ /* instructions for specific cpu's */ /* Macros for adjusting thread priority (hardware multi-threading) The defines are the same ones used by the linux kernel */ #ifdef _ARCH_PWR8 #ifdef __GLIBC__ #include <sys/platform/ppc.h> /* Very low priority */ #define HMT_very_low() __ppc_set_ppr_very_low() /* Low priority */ #define HMT_low() __ppc_set_ppr_low() /* Medium low priority */ #define HMT_medium_low() __ppc_set_ppr_med_low() /* Medium priority */ #define HMT_medium() __ppc_set_ppr_med() /* Medium high priority */ #define HMT_medium_high() __ppc_set_ppr_med_high() /* High priority */ #define HMT_high() asm volatile("or 3,3,3") #else /* GLIBC */ #if defined(__FreeBSD__) #include <sys/types.h> #include <sys/sysctl.h> #endif #define HMT_very_low() __asm__ volatile ("or 31,31,31") #define HMT_low() __asm__ volatile ("or 1,1,1") #define HMT_medium_low() __asm__ volatile ("or 6,6,6") #define HMT_medium() __asm__ volatile ("or 2,2,2") #define HMT_medium_high() __asm__ volatile ("or 5,5,5") #define HMT_high() asm volatile("or 3,3,3") #endif /* GLIBC */ #else #define HMT_very_low() #define HMT_low() #define HMT_medium_low() #define HMT_medium() #define HMT_medium_high() #define HMT_high() #endif #if defined __i386__ || defined __x86_64__ || defined _WIN32 # define HAVE_PAUSE_INSTRUCTION /* added in Intel Pentium 4 */ #endif #ifdef _WIN32 #elif defined HAVE_PAUSE_INSTRUCTION #elif defined(_ARCH_PWR8) #elif defined __GNUC__ && (defined __arm__ || defined __aarch64__) #else # include "my_global.h" # include "my_atomic.h" #endif static inline void MY_RELAX_CPU(void) { #ifdef _WIN32 /* In the Win32 API, the x86 PAUSE instruction is executed by calling the YieldProcessor macro defined in WinNT.h. It is a CPU architecture- independent way by using YieldProcessor. */ YieldProcessor(); #elif defined HAVE_PAUSE_INSTRUCTION /* According to the gcc info page, asm volatile means that the instruction has important side-effects and must not be removed. Also asm volatile may trigger a memory barrier (spilling all registers to memory). */ #ifdef __SUNPRO_CC asm ("pause" ); #else __asm__ __volatile__ ("pause"); #endif #elif defined(_ARCH_PWR8) /* Changed from __ppc_get_timebase for musl and clang compatibility */ __builtin_ppc_get_timebase(); #elif defined __GNUC__ && defined __riscv /* The GCC-only __builtin_riscv_pause() or the pause instruction is encoded like a fence instruction with special parameters. On RISC-V implementations that do not support arch=+zihintpause this instruction could be interpreted as a more expensive memory fence; it should not be an illegal instruction. */ __asm__ volatile(".long 0x0100000f" ::: "memory"); #elif defined __GNUC__ /* Mainly, prevent the compiler from optimizing away delay loops */ __asm__ __volatile__ ("":::"memory"); #endif } #ifdef HAVE_PAUSE_INSTRUCTION # ifdef __cplusplus extern "C" { # endif extern unsigned my_cpu_relax_multiplier; void my_cpu_init(void); # ifdef __cplusplus } # endif #else # define my_cpu_relax_multiplier 200 # define my_cpu_init() /* nothing */ #endif /* LF_BACKOFF should be used to improve performance on hyperthreaded CPUs. Intel recommends to use it in spin loops also on non-HT machines to reduce power consumption (see e.g http://softwarecommunity.intel.com/articles/eng/2004.htm) Running benchmarks for spinlocks implemented with InterlockedCompareExchange and YieldProcessor shows that much better performance is achieved by calling YieldProcessor in a loop - that is, yielding longer. On Intel boxes setting loop count in the range 200-300 brought best results. */ static inline int LF_BACKOFF(void) { unsigned i= my_cpu_relax_multiplier; while (i--) MY_RELAX_CPU(); return 1; } /** Run a delay loop while waiting for a shared resource to be released. @param delay originally, roughly microseconds on 100 MHz Intel Pentium */ static inline void ut_delay(unsigned delay) { unsigned i= my_cpu_relax_multiplier / 4 * delay; HMT_low(); while (i--) MY_RELAX_CPU(); HMT_medium(); } #endif
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