diff options
| author | Vineet Gupta <vgupta@kernel.org> | 2020-05-14 00:51:26 -0700 |
|---|---|---|
| committer | Vineet Gupta <vgupta@kernel.org> | 2023-08-17 20:31:59 -0700 |
| commit | fd476197c63dd3aae85e286dab7da23b159562b9 (patch) | |
| tree | d622edf6debfd6e79fe17625893b69ebfd6b0a29 /arch/arc/kernel/ctx_sw_asm.S | |
| parent | b060b7d0c105d495eb9338a3f6c7bc0c09830a2c (diff) | |
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/kernel/ctx_sw_asm.S')
| -rw-r--r-- | arch/arc/kernel/ctx_sw_asm.S | 22 |
1 files changed, 10 insertions, 12 deletions
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 <asm/entry.h> /* For the SAVE_* macros */ #include <asm/asm-offsets.h> -#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 |