Current File : //usr/include/mysql/server/private/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
#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
#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)
__ppc_get_timebase();
#elif defined __GNUC__ && (defined __arm__ || defined __aarch64__)
/* Mainly, prevent the compiler from optimizing away delay loops */
__asm__ __volatile__ ("":::"memory");
#else
int32 var, oldval = 0;
my_atomic_cas32_strong_explicit(&var, &oldval, 1, MY_MEMORY_ORDER_RELAXED,
MY_MEMORY_ORDER_RELAXED);
#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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