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powerpc: Add the ability to save FPU without giving it up

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This patch adds the ability to be able to save the FPU registers to the
thread struct without giving up (disabling the facility) next time the
process returns to userspace.

This patch optimises the thread copy path (as a result of a fork() or
clone()) so that the parent thread can return to userspace with hot
registers avoiding a possibly pointless reload of FPU register state.

Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Cyril Bur 2016-02-29 17:53:49 +11:00 committed by Michael Ellerman
parent de2a20aa72
commit 8792468da5
3 changed files with 17 additions and 19 deletions
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3
arch/powerpc/include/asm/switch_to.h
View File

@ -28,13 +28,14 @@ extern void giveup_all(struct task_struct *);
extern void enable_kernel_fp(void);
extern void flush_fp_to_thread(struct task_struct *);
extern void giveup_fpu(struct task_struct *);
extern void __giveup_fpu(struct task_struct *);
extern void save_fpu(struct task_struct *);
static inline void disable_kernel_fp(void)
{
msr_check_and_clear(MSR_FP);
}
#else
static inline void __giveup_fpu(struct task_struct *t) { }
static inline void save_fpu(struct task_struct *t) { }
static inline void flush_fp_to_thread(struct task_struct *t) { }
#endif

21
arch/powerpc/kernel/fpu.S
View File

@ -143,33 +143,20 @@ END_FTR_SECTION_IFSET(CPU_FTR_VSX)
blr
/*
* __giveup_fpu(tsk)
* Disable FP for the task given as the argument,
* and save the floating-point registers in its thread_struct.
* save_fpu(tsk)
* Save the floating-point registers in its thread_struct.
* Enables the FPU for use in the kernel on return.
*/
_GLOBAL(__giveup_fpu)
_GLOBAL(save_fpu)
addi r3,r3,THREAD /* want THREAD of task */
PPC_LL r6,THREAD_FPSAVEAREA(r3)
PPC_LL r5,PT_REGS(r3)
PPC_LCMPI 0,r6,0
bne 2f
addi r6,r3,THREAD_FPSTATE
2: PPC_LCMPI 0,r5,0
SAVE_32FPVSRS(0, R4, R6)
2: SAVE_32FPVSRS(0, R4, R6)
mffs fr0
stfd fr0,FPSTATE_FPSCR(r6)
beq 1f
PPC_LL r4,_MSR-STACK_FRAME_OVERHEAD(r5)
li r3,MSR_FP|MSR_FE0|MSR_FE1
#ifdef CONFIG_VSX
BEGIN_FTR_SECTION
oris r3,r3,MSR_VSX@h
END_FTR_SECTION_IFSET(CPU_FTR_VSX)
#endif
andc r4,r4,r3 /* disable FP for previous task */
PPC_STL r4,_MSR-STACK_FRAME_OVERHEAD(r5)
1:
blr
/*

12
arch/powerpc/kernel/process.c
View File

@ -133,6 +133,16 @@ void __msr_check_and_clear(unsigned long bits)
EXPORT_SYMBOL(__msr_check_and_clear);
#ifdef CONFIG_PPC_FPU
void __giveup_fpu(struct task_struct *tsk)
{
save_fpu(tsk);
tsk->thread.regs->msr &= ~MSR_FP;
#ifdef CONFIG_VSX
if (cpu_has_feature(CPU_FTR_VSX))
tsk->thread.regs->msr &= ~MSR_VSX;
#endif
}
void giveup_fpu(struct task_struct *tsk)
{
check_if_tm_restore_required(tsk);
@ -459,7 +469,7 @@ void save_all(struct task_struct *tsk)
msr_check_and_set(msr_all_available);
if (usermsr & MSR_FP)
__giveup_fpu(tsk);
save_fpu(tsk);
if (usermsr & MSR_VEC)
__giveup_altivec(tsk);