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riscv: entry: Split ret_from_fork() into user and kernel

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This function was unified into a single function in commit ab9164dae2
("riscv: entry: Consolidate ret_from_kernel_thread into ret_from_fork").
However that imposed a performance degradation.

Partially reverting this commit to have ret_from_fork() split again,
results in a 1% increase on the number of times fork is able to be called
per second.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/all/20250320-riscv_optimize_entry-v6-2-63e187e26041@rivosinc.com
This commit is contained in:
Charlie Jenkins 2025-03-20 10:29:22 -07:00 committed by Thomas Gleixner
parent f955aa8723
commit 5b3d6103b3
3 changed files with 23 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
arch/riscv/include/asm/asm-prototypes.h
View File

@ -52,7 +52,8 @@ DECLARE_DO_ERROR_INFO(do_trap_ecall_s);
DECLARE_DO_ERROR_INFO(do_trap_ecall_m);
DECLARE_DO_ERROR_INFO(do_trap_break);
asmlinkage void ret_from_fork(void *fn_arg, int (*fn)(void *), struct pt_regs *regs);
asmlinkage void ret_from_fork_kernel(void *fn_arg, int (*fn)(void *), struct pt_regs *regs);
asmlinkage void ret_from_fork_user(struct pt_regs *regs);
asmlinkage void handle_bad_stack(struct pt_regs *regs);
asmlinkage void do_page_fault(struct pt_regs *regs);
asmlinkage void do_irq(struct pt_regs *regs);

13
arch/riscv/kernel/entry.S
View File

@ -319,14 +319,21 @@ SYM_CODE_END(handle_kernel_stack_overflow)
ASM_NOKPROBE(handle_kernel_stack_overflow)
#endif
SYM_CODE_START(ret_from_fork_asm)
SYM_CODE_START(ret_from_fork_kernel_asm)
call schedule_tail
move a0, s1 /* fn_arg */
move a1, s0 /* fn */
move a2, sp /* pt_regs */
call ret_from_fork
call ret_from_fork_kernel
j ret_from_exception
SYM_CODE_END(ret_from_fork_asm)
SYM_CODE_END(ret_from_fork_kernel_asm)
SYM_CODE_START(ret_from_fork_user_asm)
call schedule_tail
move a0, sp /* pt_regs */
call ret_from_fork_user
j ret_from_exception
SYM_CODE_END(ret_from_fork_user_asm)
#ifdef CONFIG_IRQ_STACKS
/*

17
arch/riscv/kernel/process.c
View File

@ -38,7 +38,8 @@ unsigned long __stack_chk_guard __read_mostly;
EXPORT_SYMBOL(__stack_chk_guard);
#endif
extern asmlinkage void ret_from_fork_asm(void);
extern asmlinkage void ret_from_fork_kernel_asm(void);
extern asmlinkage void ret_from_fork_user_asm(void);
void noinstr arch_cpu_idle(void)
{
@ -208,14 +209,18 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
return 0;
}
asmlinkage void ret_from_fork(void *fn_arg, int (*fn)(void *), struct pt_regs *regs)
asmlinkage void ret_from_fork_kernel(void *fn_arg, int (*fn)(void *), struct pt_regs *regs)
{
if (unlikely(fn))
fn(fn_arg);
fn(fn_arg);
syscall_exit_to_user_mode(regs);
}
asmlinkage void ret_from_fork_user(struct pt_regs *regs)
{
syscall_exit_to_user_mode(regs);
}
int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
{
unsigned long clone_flags = args->flags;
@ -238,6 +243,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
p->thread.s[0] = (unsigned long)args->fn;
p->thread.s[1] = (unsigned long)args->fn_arg;
p->thread.ra = (unsigned long)ret_from_fork_kernel_asm;
} else {
*childregs = *(current_pt_regs());
/* Turn off status.VS */
@ -247,12 +253,11 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
if (clone_flags & CLONE_SETTLS)
childregs->tp = tls;
childregs->a0 = 0; /* Return value of fork() */
p->thread.s[0] = 0;
p->thread.ra = (unsigned long)ret_from_fork_user_asm;
}
p->thread.riscv_v_flags = 0;
if (has_vector() || has_xtheadvector())
riscv_v_thread_alloc(p);
p->thread.ra = (unsigned long)ret_from_fork_asm;
p->thread.sp = (unsigned long)childregs; /* kernel sp */
return 0;
}