From cfca4b5abe0cc13f9d9f45f760efd8260e31200f Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Tue, 12 May 2020 22:18:08 -0700 Subject: ARC: entry: use gp to cache task pointer (vs. r25) The motivation is eventual ABI considerations for ARCv3 but even without it this change us worthwhile as diffstat reduces 100 net lines r25 is a callee saved register, normally not saved by entry code in pt_regs. However because of its usage in CONFIG_ARC_CURR_IN_REG it needs to be. This in turn requires a whole bunch of special casing when we need to access r25. Then there is distinction between user mode r25 vs. kernel mode r25 - hence distinct SAVE_CALLEE_SAVED_{USER,KERNEL} Instead use gp which is a scratch register and thus saved already in entry code. This cleans things up significantly and much nocer on eyes: - SAVE_CALLEE_SAVED_{USER,KERNEL} are now exactly same - no special user_r25 slot in pt_reggs Note that typical global asm registers are callee-saved (r25), but gp is not callee-saved thus needs additional -ffixed- toggle Signed-off-by: Vineet Gupta --- arch/arc/kernel/process.c | 11 ----------- 1 file changed, 11 deletions(-) (limited to 'arch/arc/kernel/process.c') diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c index 980b71da2f61..96f591508142 100644 --- a/arch/arc/kernel/process.c +++ b/arch/arc/kernel/process.c @@ -162,7 +162,6 @@ asmlinkage void ret_from_fork(void); * | SP | * | orig_r0 | * | event/ECR | - * | user_r25 | * ------------------ <===== END of PAGE */ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) @@ -243,16 +242,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) */ c_callee->r25 = task_thread_info(p)->thr_ptr; -#ifdef CONFIG_ARC_CURR_IN_REG - /* - * setup usermode thread pointer #2: - * however for this special use of r25 in kernel, __switch_to() sets - * r25 for kernel needs and only in the final return path is usermode - * r25 setup, from pt_regs->user_r25. So set that up as well - */ - c_regs->user_r25 = c_callee->r25; -#endif - return 0; } -- cgit v1.2.3 From fd476197c63dd3aae85e286dab7da23b159562b9 Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Thu, 14 May 2020 00:51:26 -0700 Subject: ARC: __switch_to: move ksp to thread_info from thread_struct task's arch specific bits are carried in 2 places - embedded thread_struct in task_struct - associated thread_info (hoisted in task's stack page) and syntactically: (thread_info *)(task_struct->stack) ksp (dynamic kernel stack top) currently lives in thread_struct but given its deep location in task struct likely to cache miss when accessed from __switch_to(). Moving it to thread_info would be more efficient given proximity to frequently accessed items such as preempt_count thus very likely to be in cache, specially in schedular code. Note however that currently tsk.thread.ksp takes 1 memory access (off of tsk pointer) while new code tsk->stack.ksp would take 2, but likely to be in cache. Moreover if task is current the 2nd reference can be elided and instead derived from SP as (SP & ~(THREAD_SIZE - 1)) All of this also makes __switch_to() code simpler and we can see the 2 ways of retirving ksp (descrobed above) in new code. Signed-off-by: Vineet Gupta --- arch/arc/include/asm/processor.h | 3 +-- arch/arc/include/asm/thread_info.h | 10 +++++----- arch/arc/kernel/asm-offsets.c | 2 +- arch/arc/kernel/ctx_sw_asm.S | 22 ++++++++++------------ arch/arc/kernel/process.c | 6 +++--- 5 files changed, 20 insertions(+), 23 deletions(-) (limited to 'arch/arc/kernel/process.c') diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h index 82ddc929d6e7..d606658e2fe7 100644 --- a/arch/arc/include/asm/processor.h +++ b/arch/arc/include/asm/processor.h @@ -22,7 +22,6 @@ * struct thread_info */ struct thread_struct { - unsigned long ksp; /* kernel mode stack pointer */ unsigned long callee_reg; /* pointer to callee regs */ unsigned long fault_address; /* dbls as brkpt holder as well */ #ifdef CONFIG_ARC_DSP_SAVE_RESTORE_REGS @@ -54,7 +53,7 @@ struct task_struct; * Where about of Task's sp, fp, blink when it was last seen in kernel mode. * Look in process.c for details of kernel stack layout */ -#define TSK_K_ESP(tsk) (tsk->thread.ksp) +#define TSK_K_ESP(tsk) (task_thread_info(tsk)->ksp) #define TSK_K_REG(tsk, off) (*((unsigned long *)(TSK_K_ESP(tsk) + \ sizeof(struct callee_regs) + off))) diff --git a/arch/arc/include/asm/thread_info.h b/arch/arc/include/asm/thread_info.h index 6ba7fe417095..4c530cf131f3 100644 --- a/arch/arc/include/asm/thread_info.h +++ b/arch/arc/include/asm/thread_info.h @@ -37,16 +37,16 @@ */ struct thread_info { unsigned long flags; /* low level flags */ + unsigned long ksp; /* kernel mode stack top in __switch_to */ int preempt_count; /* 0 => preemptable, <0 => BUG */ - struct task_struct *task; /* main task structure */ - __u32 cpu; /* current CPU */ + int cpu; /* current CPU */ unsigned long thr_ptr; /* TLS ptr */ + struct task_struct *task; /* main task structure */ }; /* - * macros/functions for gaining access to the thread information structure - * - * preempt_count needs to be 1 initially, until the scheduler is functional. + * initilaize thread_info for any @tsk + * - this is not related to init_task per se */ #define INIT_THREAD_INFO(tsk) \ { \ diff --git a/arch/arc/kernel/asm-offsets.c b/arch/arc/kernel/asm-offsets.c index 37324fd9a72f..5b47d09b925e 100644 --- a/arch/arc/kernel/asm-offsets.c +++ b/arch/arc/kernel/asm-offsets.c @@ -20,13 +20,13 @@ int main(void) BLANK(); - DEFINE(THREAD_KSP, offsetof(struct thread_struct, ksp)); DEFINE(THREAD_CALLEE_REG, offsetof(struct thread_struct, callee_reg)); DEFINE(THREAD_FAULT_ADDR, offsetof(struct thread_struct, fault_address)); BLANK(); + DEFINE(THREAD_INFO_KSP, offsetof(struct thread_info, ksp)); DEFINE(THREAD_INFO_FLAGS, offsetof(struct thread_info, flags)); DEFINE(THREAD_INFO_PREEMPT_COUNT, offsetof(struct thread_info, preempt_count)); diff --git a/arch/arc/kernel/ctx_sw_asm.S b/arch/arc/kernel/ctx_sw_asm.S index 59d779004e64..48e1f21976ed 100644 --- a/arch/arc/kernel/ctx_sw_asm.S +++ b/arch/arc/kernel/ctx_sw_asm.S @@ -11,8 +11,6 @@ #include /* For the SAVE_* macros */ #include -#define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4) - ; IN ; - r0: prev task (also current) ; - r1: next task @@ -37,19 +35,19 @@ ENTRY_CFI(__switch_to) /* kernel mode callee regs of @prev */ SAVE_CALLEE_SAVED_KERNEL - /* save final SP to @prev->thread.ksp */ -#if KSP_WORD_OFF <= 255 - st.as sp, [r0, KSP_WORD_OFF] -#else - /* Workaround for NR_CPUS=4k as ST.as can only take s9 offset */ - add2 r10, r0, KSP_WORD_OFF - st sp, [r10] -#endif + /* + * save final SP to @prev->thread_info.ksp + * @prev is "current" so thread_info derived from SP + */ + GET_CURR_THR_INFO_FROM_SP r10 + st sp, [r10, THREAD_INFO_KSP] + /* update @next in _current_task[] and GP register caching it */ SET_CURR_TASK_ON_CPU r1, r10 - /* load SP from @next->thread.ksp */ - ld.as sp, [r1, KSP_WORD_OFF] + /* load SP from @next->thread_info.ksp */ + ld r10, [r1, TASK_THREAD_INFO] + ld sp, [r10, THREAD_INFO_KSP] /* restore callee regs, stack frame regs of @next */ RESTORE_CALLEE_SAVED_KERNEL diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c index 96f591508142..186ceab661eb 100644 --- a/arch/arc/kernel/process.c +++ b/arch/arc/kernel/process.c @@ -141,7 +141,7 @@ asmlinkage void ret_from_fork(void); * | unused | * | | * ------------------ - * | r25 | <==== top of Stack (thread.ksp) + * | r25 | <==== top of Stack (thread_info.ksp) * ~ ~ * | --to-- | (CALLEE Regs of kernel mode) * | r13 | @@ -181,14 +181,14 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) c_callee = ((struct callee_regs *)childksp) - 1; /* - * __switch_to() uses thread.ksp to start unwinding stack + * __switch_to() uses thread_info.ksp to start unwinding stack * For kernel threads we don't need to create callee regs, the * stack layout nevertheless needs to remain the same. * Also, since __switch_to anyways unwinds callee regs, we use * this to populate kernel thread entry-pt/args into callee regs, * so that ret_from_kernel_thread() becomes simpler. */ - p->thread.ksp = (unsigned long)c_callee; /* THREAD_KSP */ + task_thread_info(p)->ksp = (unsigned long)c_callee; /* THREAD_INFO_KSP */ /* __switch_to expects FP(0), BLINK(return addr) at top */ childksp[0] = 0; /* fp */ -- cgit v1.2.3