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RISC-V: Add _TIF_NEED_RESCHED check for kernel thread when CONFIG_PREEMPT=y

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The cond_resched() can be used to yield the CPU resource if
CONFIG_PREEMPT is not defined. Otherwise, cond_resched() is a dummy
function. In order to avoid kernel thread occupying entire CPU,
when CONFIG_PREEMPT=y, the kernel thread needs to follow the
rescheduling mechanism like a user thread.

Signed-off-by: Vincent Chen <vincentc@andestech.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
This commit is contained in:
Vincent Chen 2019-01-03 11:32:33 +08:00 committed by Palmer Dabbelt
parent 49a57857ae
commit 99fd6e875d
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GPG Key ID: EF4CA1502CCBAB41
2 changed files with 18 additions and 1 deletions
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1
arch/riscv/kernel/asm-offsets.c
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@ -39,6 +39,7 @@ void asm_offsets(void)
OFFSET(TASK_STACK, task_struct, stack);
OFFSET(TASK_TI, task_struct, thread_info);
OFFSET(TASK_TI_FLAGS, task_struct, thread_info.flags);
OFFSET(TASK_TI_PREEMPT_COUNT, task_struct, thread_info.preempt_count);
OFFSET(TASK_TI_KERNEL_SP, task_struct, thread_info.kernel_sp);
OFFSET(TASK_TI_USER_SP, task_struct, thread_info.user_sp);
OFFSET(TASK_TI_CPU, task_struct, thread_info.cpu);

18
arch/riscv/kernel/entry.S
View File

@ -144,6 +144,10 @@ _save_context:
REG_L x2, PT_SP(sp)
.endm
#if !IS_ENABLED(CONFIG_PREEMPT)
.set resume_kernel, restore_all
#endif
ENTRY(handle_exception)
SAVE_ALL
@ -228,7 +232,7 @@ ret_from_exception:
REG_L s0, PT_SSTATUS(sp)
csrc sstatus, SR_SIE
andi s0, s0, SR_SPP
bnez s0, restore_all
bnez s0, resume_kernel
resume_userspace:
/* Interrupts must be disabled here so flags are checked atomically */
@ -250,6 +254,18 @@ restore_all:
RESTORE_ALL
sret
#if IS_ENABLED(CONFIG_PREEMPT)
resume_kernel:
REG_L s0, TASK_TI_PREEMPT_COUNT(tp)
bnez s0, restore_all
need_resched:
REG_L s0, TASK_TI_FLAGS(tp)
andi s0, s0, _TIF_NEED_RESCHED
beqz s0, restore_all
call preempt_schedule_irq
j need_resched
#endif
work_pending:
/* Enter slow path for supplementary processing */
la ra, ret_from_exception