From 152d523e6307c7152f9986a542f873b5c5863937 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Thu, 29 Oct 2015 11:43:55 +1100 Subject: [PATCH] powerpc: Create context switch helpers save_sprs() and restore_sprs() Move all our context switch SPR save and restore code into two helpers. We do a few optimisations: - Group all mfsprs and all mtsprs. In many cases an mtspr sets a scoreboarding bit that an mfspr waits on, so the current practise of mfspr A; mtspr A; mfpsr B; mtspr B is the worst scheduling we can do. - SPR writes are slow, so check that the value is changing before writing it. A context switch microbenchmark using yield(): http://ozlabs.org/~anton/junkcode/context_switch2.c ./context_switch2 --test=yield 0 0 shows an improvement of almost 10% on POWER8. Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/processor.h | 1 + arch/powerpc/include/asm/switch_to.h | 11 ---- arch/powerpc/kernel/entry_64.S | 60 +----------------- arch/powerpc/kernel/process.c | 92 ++++++++++++++++++++++++---- 4 files changed, 82 insertions(+), 82 deletions(-) diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h index 5afea361beaa..c273f3e0ba84 100644 --- a/arch/powerpc/include/asm/processor.h +++ b/arch/powerpc/include/asm/processor.h @@ -294,6 +294,7 @@ struct thread_struct { #endif #ifdef CONFIG_PPC64 unsigned long dscr; + unsigned long fscr; /* * This member element dscr_inherit indicates that the process * has explicitly attempted and changed the DSCR register value diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h index 15cca17cba4b..33a071d24ba8 100644 --- a/arch/powerpc/include/asm/switch_to.h +++ b/arch/powerpc/include/asm/switch_to.h @@ -15,17 +15,6 @@ extern struct task_struct *__switch_to(struct task_struct *, struct thread_struct; extern struct task_struct *_switch(struct thread_struct *prev, struct thread_struct *next); -#ifdef CONFIG_PPC_BOOK3S_64 -static inline void save_early_sprs(struct thread_struct *prev) -{ - if (cpu_has_feature(CPU_FTR_ARCH_207S)) - prev->tar = mfspr(SPRN_TAR); - if (cpu_has_feature(CPU_FTR_DSCR)) - prev->dscr = mfspr(SPRN_DSCR); -} -#else -static inline void save_early_sprs(struct thread_struct *prev) {} -#endif extern void enable_kernel_fp(void); extern void enable_kernel_altivec(void); diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 93bb284fddf9..e84e5bc7fe34 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -453,29 +453,12 @@ _GLOBAL(_switch) SAVE_8GPRS(14, r1) SAVE_10GPRS(22, r1) mflr r20 /* Return to switch caller */ -#ifdef CONFIG_ALTIVEC -BEGIN_FTR_SECTION - mfspr r24,SPRN_VRSAVE /* save vrsave register value */ - std r24,THREAD_VRSAVE(r3) -END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC) -#endif /* CONFIG_ALTIVEC */ + std r20,_NIP(r1) mfcr r23 std r23,_CCR(r1) std r1,KSP(r3) /* Set old stack pointer */ -#ifdef CONFIG_PPC_BOOK3S_64 -BEGIN_FTR_SECTION - /* Event based branch registers */ - mfspr r0, SPRN_BESCR - std r0, THREAD_BESCR(r3) - mfspr r0, SPRN_EBBHR - std r0, THREAD_EBBHR(r3) - mfspr r0, SPRN_EBBRR - std r0, THREAD_EBBRR(r3) -END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) -#endif - #ifdef CONFIG_SMP /* We need a sync somewhere here to make sure that if the * previous task gets rescheduled on another CPU, it sees all @@ -563,47 +546,6 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_1T_SEGMENT) mr r1,r8 /* start using new stack pointer */ std r7,PACAKSAVE(r13) -#ifdef CONFIG_PPC_BOOK3S_64 -BEGIN_FTR_SECTION - /* Event based branch registers */ - ld r0, THREAD_BESCR(r4) - mtspr SPRN_BESCR, r0 - ld r0, THREAD_EBBHR(r4) - mtspr SPRN_EBBHR, r0 - ld r0, THREAD_EBBRR(r4) - mtspr SPRN_EBBRR, r0 - - ld r0,THREAD_TAR(r4) - mtspr SPRN_TAR,r0 -END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S) -#endif - -#ifdef CONFIG_ALTIVEC -BEGIN_FTR_SECTION - ld r0,THREAD_VRSAVE(r4) - mtspr SPRN_VRSAVE,r0 /* if G4, restore VRSAVE reg */ -END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC) -#endif /* CONFIG_ALTIVEC */ -#ifdef CONFIG_PPC64 -BEGIN_FTR_SECTION - lwz r6,THREAD_DSCR_INHERIT(r4) - ld r0,THREAD_DSCR(r4) - cmpwi r6,0 - bne 1f - ld r0,PACA_DSCR_DEFAULT(r13) -1: -BEGIN_FTR_SECTION_NESTED(70) - mfspr r8, SPRN_FSCR - rldimi r8, r6, FSCR_DSCR_LG, (63 - FSCR_DSCR_LG) - mtspr SPRN_FSCR, r8 -END_FTR_SECTION_NESTED(CPU_FTR_ARCH_207S, CPU_FTR_ARCH_207S, 70) - cmpd r0,r25 - beq 2f - mtspr SPRN_DSCR,r0 -2: -END_FTR_SECTION_IFSET(CPU_FTR_DSCR) -#endif - ld r6,_CCR(r1) mtcrf 0xFF,r6 diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 75b6676c1a0b..3aabed4a60a9 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -742,6 +742,73 @@ void restore_tm_state(struct pt_regs *regs) #define __switch_to_tm(prev) #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */ +static inline void save_sprs(struct thread_struct *t) +{ +#ifdef CONFIG_ALTIVEC + if (cpu_has_feature(cpu_has_feature(CPU_FTR_ALTIVEC))) + t->vrsave = mfspr(SPRN_VRSAVE); +#endif +#ifdef CONFIG_PPC_BOOK3S_64 + if (cpu_has_feature(CPU_FTR_DSCR)) + t->dscr = mfspr(SPRN_DSCR); + + if (cpu_has_feature(CPU_FTR_ARCH_207S)) { + t->bescr = mfspr(SPRN_BESCR); + t->ebbhr = mfspr(SPRN_EBBHR); + t->ebbrr = mfspr(SPRN_EBBRR); + + t->fscr = mfspr(SPRN_FSCR); + + /* + * Note that the TAR is not available for use in the kernel. + * (To provide this, the TAR should be backed up/restored on + * exception entry/exit instead, and be in pt_regs. FIXME, + * this should be in pt_regs anyway (for debug).) + */ + t->tar = mfspr(SPRN_TAR); + } +#endif +} + +static inline void restore_sprs(struct thread_struct *old_thread, + struct thread_struct *new_thread) +{ +#ifdef CONFIG_ALTIVEC + if (cpu_has_feature(CPU_FTR_ALTIVEC) && + old_thread->vrsave != new_thread->vrsave) + mtspr(SPRN_VRSAVE, new_thread->vrsave); +#endif +#ifdef CONFIG_PPC_BOOK3S_64 + if (cpu_has_feature(CPU_FTR_DSCR)) { + u64 dscr = get_paca()->dscr_default; + u64 fscr = old_thread->fscr & ~FSCR_DSCR; + + if (new_thread->dscr_inherit) { + dscr = new_thread->dscr; + fscr |= FSCR_DSCR; + } + + if (old_thread->dscr != dscr) + mtspr(SPRN_DSCR, dscr); + + if (old_thread->fscr != fscr) + mtspr(SPRN_FSCR, fscr); + } + + if (cpu_has_feature(CPU_FTR_ARCH_207S)) { + if (old_thread->bescr != new_thread->bescr) + mtspr(SPRN_BESCR, new_thread->bescr); + if (old_thread->ebbhr != new_thread->ebbhr) + mtspr(SPRN_EBBHR, new_thread->ebbhr); + if (old_thread->ebbrr != new_thread->ebbrr) + mtspr(SPRN_EBBRR, new_thread->ebbrr); + + if (old_thread->tar != new_thread->tar) + mtspr(SPRN_TAR, new_thread->tar); + } +#endif +} + struct task_struct *__switch_to(struct task_struct *prev, struct task_struct *new) { @@ -751,17 +818,16 @@ struct task_struct *__switch_to(struct task_struct *prev, struct ppc64_tlb_batch *batch; #endif + new_thread = &new->thread; + old_thread = ¤t->thread; + WARN_ON(!irqs_disabled()); - /* Back up the TAR and DSCR across context switches. - * Note that the TAR is not available for use in the kernel. (To - * provide this, the TAR should be backed up/restored on exception - * entry/exit instead, and be in pt_regs. FIXME, this should be in - * pt_regs anyway (for debug).) - * Save the TAR and DSCR here before we do treclaim/trecheckpoint as - * these will change them. + /* + * We need to save SPRs before treclaim/trecheckpoint as these will + * change a number of them. */ - save_early_sprs(&prev->thread); + save_sprs(&prev->thread); __switch_to_tm(prev); @@ -844,10 +910,6 @@ struct task_struct *__switch_to(struct task_struct *prev, #endif /* CONFIG_HAVE_HW_BREAKPOINT */ #endif - - new_thread = &new->thread; - old_thread = ¤t->thread; - #ifdef CONFIG_PPC64 /* * Collect processor utilization data per process @@ -883,6 +945,10 @@ struct task_struct *__switch_to(struct task_struct *prev, last = _switch(old_thread, new_thread); + /* Need to recalculate these after calling _switch() */ + old_thread = &last->thread; + new_thread = ¤t->thread; + #ifdef CONFIG_PPC_BOOK3S_64 if (current_thread_info()->local_flags & _TLF_LAZY_MMU) { current_thread_info()->local_flags &= ~_TLF_LAZY_MMU; @@ -891,6 +957,8 @@ struct task_struct *__switch_to(struct task_struct *prev, } #endif /* CONFIG_PPC_BOOK3S_64 */ + restore_sprs(old_thread, new_thread); + return last; } -- 2.39.5