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| author | Vineet Gupta <vgupta@kernel.org> | 2020-05-14 10:51:26 +0300 |
|---|---|---|
| committer | Vineet Gupta <vgupta@kernel.org> | 2023-08-18 06:31:59 +0300 |
| commit | fd476197c63dd3aae85e286dab7da23b159562b9 (patch) | |
| tree | d622edf6debfd6e79fe17625893b69ebfd6b0a29 /arch/arc/include/asm | |
| parent | b060b7d0c105d495eb9338a3f6c7bc0c09830a2c (diff) | |
| download | linux-fd476197c63dd3aae85e286dab7da23b159562b9.tar.xz | |
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 <vgupta@kernel.org>
Diffstat (limited to 'arch/arc/include/asm')
| -rw-r--r-- | arch/arc/include/asm/processor.h | 3 | ||||
| -rw-r--r-- | arch/arc/include/asm/thread_info.h | 10 |
2 files changed, 6 insertions, 7 deletions
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) \ { \ |