root/arch/x86/include/asm/mwait.h

DEFINITIONS

1. __monitor
2. __mwait
3. mwait_idle_with_hints

#ifndef _ASM_X86_MWAIT_H
#define _ASM_X86_MWAIT_H

#include <linux/sched.h>

#define MWAIT_SUBSTATE_MASK             0xf
#define MWAIT_CSTATE_MASK               0xf
#define MWAIT_SUBSTATE_SIZE             4
#define MWAIT_HINT2CSTATE(hint)         (((hint) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK)
#define MWAIT_HINT2SUBSTATE(hint)       ((hint) & MWAIT_CSTATE_MASK)

#define CPUID_MWAIT_LEAF                5
#define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1
#define CPUID5_ECX_INTERRUPT_BREAK      0x2

#define MWAIT_ECX_INTERRUPT_BREAK       0x1

static inline void __monitor(const void *eax, unsigned long ecx,
                             unsigned long edx)
{
        /* "monitor %eax, %ecx, %edx;" */
        asm volatile(".byte 0x0f, 0x01, 0xc8;"
                     :: "a" (eax), "c" (ecx), "d"(edx));
}

static inline void __mwait(unsigned long eax, unsigned long ecx)
{
        /* "mwait %eax, %ecx;" */
        asm volatile(".byte 0x0f, 0x01, 0xc9;"
                     :: "a" (eax), "c" (ecx));
}

/*
 * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
 * which can obviate IPI to trigger checking of need_resched.
 * We execute MONITOR against need_resched and enter optimized wait state
 * through MWAIT. Whenever someone changes need_resched, we would be woken
 * up from MWAIT (without an IPI).
 *
 * New with Core Duo processors, MWAIT can take some hints based on CPU
 * capability.
 */
static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx)
{
        if (!current_set_polling_and_test()) {
                if (static_cpu_has_bug(X86_BUG_CLFLUSH_MONITOR)) {
                        mb();
                        clflush((void *)&current_thread_info()->flags);
                        mb();
                }

                __monitor((void *)&current_thread_info()->flags, 0, 0);
                if (!need_resched())
                        __mwait(eax, ecx);
        }
        current_clr_polling();
}

#endif /* _ASM_X86_MWAIT_H */