switch_to.h

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/*
 * Low-level task switching. This is based on information published in
 * the Processor Abstraction Layer and the System Abstraction Layer
 * manual.
 *
 * Copyright (C) 1998-2003 Hewlett-Packard Co
 *  David Mosberger-Tang <[email protected]>
 * Copyright (C) 1999 Asit Mallick <[email protected]>
 * Copyright (C) 1999 Don Dugger <[email protected]>
 */
#ifndef _ASM_IA64_SWITCH_TO_H
#define _ASM_IA64_SWITCH_TO_H

#include <linux/percpu.h>

struct task_struct;

/*
 * Context switch from one thread to another.  If the two threads have
 * different address spaces, schedule() has already taken care of
 * switching to the new address space by calling switch_mm().
 *
 * Disabling access to the fph partition and the debug-register
 * context switch MUST be done before calling ia64_switch_to() since a
 * newly created thread returns directly to
 * ia64_ret_from_syscall_clear_r8.
 */
extern struct task_struct *ia64_switch_to (void *next_task);

extern void ia64_save_extra (struct task_struct *task);
extern void ia64_load_extra (struct task_struct *task);

#ifdef CONFIG_PERFMON
  DECLARE_PER_CPU(unsigned long, pfm_syst_info);
# define PERFMON_IS_SYSWIDE() (__get_cpu_var(pfm_syst_info) & 0x1)
#else
# define PERFMON_IS_SYSWIDE() (0)
#endif

#define IA64_HAS_EXTRA_STATE(t)                         \
    ((t)->thread.flags & (IA64_THREAD_DBG_VALID|IA64_THREAD_PM_VALID)   \
     || PERFMON_IS_SYSWIDE())

#define __switch_to(prev,next,last) do {                             \
    if (IA64_HAS_EXTRA_STATE(prev))                              \
        ia64_save_extra(prev);                               \
    if (IA64_HAS_EXTRA_STATE(next))                              \
        ia64_load_extra(next);                               \
    ia64_psr(task_pt_regs(next))->dfh = !ia64_is_local_fpu_owner(next);          \
    (last) = ia64_switch_to((next));                             \
} while (0)

#ifdef CONFIG_SMP
/*
 * In the SMP case, we save the fph state when context-switching away from a thread that
 * modified fph.  This way, when the thread gets scheduled on another CPU, the CPU can
 * pick up the state from task->thread.fph, avoiding the complication of having to fetch
 * the latest fph state from another CPU.  In other words: eager save, lazy restore.
 */
# define switch_to(prev,next,last) do {                     \
    if (ia64_psr(task_pt_regs(prev))->mfh && ia64_is_local_fpu_owner(prev)) {               \
        ia64_psr(task_pt_regs(prev))->mfh = 0;          \
        (prev)->thread.flags |= IA64_THREAD_FPH_VALID;          \
        __ia64_save_fpu((prev)->thread.fph);                \
    }                                   \
    __switch_to(prev, next, last);                      \
    /* "next" in old context is "current" in new context */         \
    if (unlikely((current->thread.flags & IA64_THREAD_MIGRATION) &&        \
             (task_cpu(current) !=                     \
                          task_thread_info(current)->last_cpu))) { \
        platform_migrate(current);                     \
        task_thread_info(current)->last_cpu = task_cpu(current);       \
    }                                      \
} while (0)
#else
# define switch_to(prev,next,last)  __switch_to(prev, next, last)
#endif

#endif /* _ASM_IA64_SWITCH_TO_H */