From fd476197c63dd3aae85e286dab7da23b159562b9 Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Thu, 14 May 2020 00:51:26 -0700 Subject: [PATCH] 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(-) diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h index 82ddc92..d606658 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 6ba7fe4..4c530cf 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 37324fd..5b47d09 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 59d7790..48e1f21 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 96f5915..186ceab 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 */ -- 2.7.4