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Linux/arch/ia64/include/asm/switch_to.h

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  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 */
 80 

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