arch/ia64/include/asm/switch_to.h

   1 /*
   2  * Low-level task switching. This is based on information published in
   3  * the Processor Abstraction Layer and the System Abstraction Layer
   4  * manual.
   5  *
   6  * Copyright (C) 1998-2003 Hewlett-Packard Co
   7  *      David Mosberger-Tang <davidm@hpl.hp.com>
   8  * Copyright (C) 1999 Asit Mallick <asit.k.mallick@intel.com>
   9  * Copyright (C) 1999 Don Dugger <don.dugger@intel.com>
  10  */
  11 #ifndef _ASM_IA64_SWITCH_TO_H
  12 #define _ASM_IA64_SWITCH_TO_H
  13
  14 #include <linux/percpu.h>
  15
  16 struct task_struct;
  17
  18 /*
  19  * Context switch from one thread to another.  If the two threads have
  20  * different address spaces, schedule() has already taken care of
  21  * switching to the new address space by calling switch_mm().
  22  *
  23  * Disabling access to the fph partition and the debug-register
  24  * context switch MUST be done before calling ia64_switch_to() since a
  25  * newly created thread returns directly to
  26  * ia64_ret_from_syscall_clear_r8.
  27  */
  28 extern struct task_struct *ia64_switch_to (void *next_task);
  29
  30 extern void ia64_save_extra (struct task_struct *task);
  31 extern void ia64_load_extra (struct task_struct *task);
  32
  33 #ifdef CONFIG_PERFMON
  34   DECLARE_PER_CPU(unsigned long, pfm_syst_info);
  35 # define PERFMON_IS_SYSWIDE() (__this_cpu_read(pfm_syst_info) & 0x1)
  36 #else
  37 # define PERFMON_IS_SYSWIDE() (0)
  38 #endif
  39
  40 #define IA64_HAS_EXTRA_STATE(t)                                                 \
  41         ((t)->thread.flags & (IA64_THREAD_DBG_VALID|IA64_THREAD_PM_VALID)       \
  42          || PERFMON_IS_SYSWIDE())
  43
  44 #define __switch_to(prev,next,last) do {                                                         \
  45         if (IA64_HAS_EXTRA_STATE(prev))                                                          \
  46                 ia64_save_extra(prev);                                                           \
  47         if (IA64_HAS_EXTRA_STATE(next))                                                          \
  48                 ia64_load_extra(next);                                                           \
  49         ia64_psr(task_pt_regs(next))->dfh = !ia64_is_local_fpu_owner(next);                      \
  50         (last) = ia64_switch_to((next));                                                         \
  51 } while (0)
  52
  53 #ifdef CONFIG_SMP
  54 /*
  55  * In the SMP case, we save the fph state when context-switching away from a thread that
  56  * modified fph.  This way, when the thread gets scheduled on another CPU, the CPU can
  57  * pick up the state from task->thread.fph, avoiding the complication of having to fetch
  58  * the latest fph state from another CPU.  In other words: eager save, lazy restore.
  59  */
  60 # define switch_to(prev,next,last) do {                                         \
  61         if (ia64_psr(task_pt_regs(prev))->mfh && ia64_is_local_fpu_owner(prev)) {                               \
  62                 ia64_psr(task_pt_regs(prev))->mfh = 0;                  \
  63                 (prev)->thread.flags |= IA64_THREAD_FPH_VALID;                  \
  64                 __ia64_save_fpu((prev)->thread.fph);                            \
  65         }                                                                       \
  66         __switch_to(prev, next, last);                                          \
  67         /* "next" in old context is "current" in new context */                 \
  68         if (unlikely((current->thread.flags & IA64_THREAD_MIGRATION) &&        \
  69                      (task_cpu(current) !=                                     \
  70                                       task_thread_info(current)->last_cpu))) { \
  71                 platform_migrate(current);                                     \
  72                 task_thread_info(current)->last_cpu = task_cpu(current);       \
  73         }                                                                      \
  74 } while (0)
  75 #else
  76 # define switch_to(prev,next,last)      __switch_to(prev, next, last)
  77 #endif
  78
  79 #endif /* _ASM_IA64_SWITCH_TO_H */