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Thu, 20 Mar 2025 10:29:36 -0700 (PDT) From: Charlie Jenkins Date: Thu, 20 Mar 2025 10:29:22 -0700 Subject: [PATCH v6 2/4] riscv: entry: Split ret_from_fork() into user and kernel Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250320-riscv_optimize_entry-v6-2-63e187e26041@rivosinc.com> References: <20250320-riscv_optimize_entry-v6-0-63e187e26041@rivosinc.com> In-Reply-To: <20250320-riscv_optimize_entry-v6-0-63e187e26041@rivosinc.com> To: Paul Walmsley , Palmer Dabbelt , Huacai Chen , WANG Xuerui , Thomas Gleixner , Peter Zijlstra , Andy Lutomirski , Alexandre Ghiti , Arnd Bergmann , Albert Ou , Alexandre Ghiti Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, Charlie Jenkins X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=4464; i=charlie@rivosinc.com; h=from:subject:message-id; bh=LoTSopBOka5A9kpDiPFFurbF+1mjOb81UBycxnBlNbA=; b=owGbwMvMwCXWx5hUnlvL8Y3xtFoSQ/qdgKoixkOt4od/iEifL9zYlhO5zOWE7Vw5m4ApZ998y O14lMvdUcrCIMbFICumyMJzrYG59Y5+2VHRsgkwc1iZQIYwcHEKwEQ2pDL8d4p6u1r9XZ/p36Ph jJrvuJPnX6/4mvmoWWO2f7i9ULmTNcNfuVlX/l06sK2ofs2Kdtmgf/l/nq4y9epjOXvN4/StFeu UuAA= X-Developer-Key: i=charlie@rivosinc.com; a=openpgp; fpr=7D834FF11B1D8387E61C776FFB10D1F27D6B1354 This function was unified into a single function in commit ab9164dae273 ("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 Acked-by: Alexandre Ghiti --- arch/riscv/include/asm/asm-prototypes.h | 3 ++- arch/riscv/kernel/entry.S | 13 ++++++++++--- arch/riscv/kernel/process.c | 17 +++++++++++------ 3 files changed, 23 insertions(+), 10 deletions(-) diff --git a/arch/riscv/include/asm/asm-prototypes.h b/arch/riscv/include/a= sm/asm-prototypes.h index 733ff609778797001006c33bba9e3cc5b1f15387..bfc8ea5f9319b19449ec59493b4= 5b926df888832 100644 --- a/arch/riscv/include/asm/asm-prototypes.h +++ b/arch/riscv/include/asm/asm-prototypes.h @@ -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); =20 -asmlinkage void ret_from_fork(void *fn_arg, int (*fn)(void *), struct pt_r= egs *regs); +asmlinkage void ret_from_fork_kernel(void *fn_arg, int (*fn)(void *), stru= ct 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); diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S index b2dc5e7c7b3a843fa4aa02eba2a911eb3ce31d1f..0fb338000c6dc0358742cd03497= fa54b9e9d1aec 100644 --- a/arch/riscv/kernel/entry.S +++ b/arch/riscv/kernel/entry.S @@ -319,14 +319,21 @@ SYM_CODE_END(handle_kernel_stack_overflow) ASM_NOKPROBE(handle_kernel_stack_overflow) #endif =20 -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) =20 #ifdef CONFIG_IRQ_STACKS /* diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index 7b0a0bfe29aec896c2bdd8976d855dd390de88d7..485ec7a80a56097e8905cd6395a= f29633846b5c8 100644 --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -38,7 +38,8 @@ unsigned long __stack_chk_guard __read_mostly; EXPORT_SYMBOL(__stack_chk_guard); #endif =20 -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); =20 void noinstr arch_cpu_idle(void) { @@ -208,14 +209,18 @@ int arch_dup_task_struct(struct task_struct *dst, str= uct task_struct *src) return 0; } =20 -asmlinkage void ret_from_fork(void *fn_arg, int (*fn)(void *), struct pt_r= egs *regs) +asmlinkage void ret_from_fork_kernel(void *fn_arg, int (*fn)(void *), stru= ct pt_regs *regs) { - if (unlikely(fn)) - fn(fn_arg); + fn(fn_arg); =20 syscall_exit_to_user_mode(regs); } =20 +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 *arg= s) { unsigned long clone_flags =3D args->flags; @@ -238,6 +243,7 @@ int copy_thread(struct task_struct *p, const struct ker= nel_clone_args *args) =20 p->thread.s[0] =3D (unsigned long)args->fn; p->thread.s[1] =3D (unsigned long)args->fn_arg; + p->thread.ra =3D (unsigned long)ret_from_fork_kernel_asm; } else { *childregs =3D *(current_pt_regs()); /* Turn off status.VS */ @@ -247,12 +253,11 @@ int copy_thread(struct task_struct *p, const struct k= ernel_clone_args *args) if (clone_flags & CLONE_SETTLS) childregs->tp =3D tls; childregs->a0 =3D 0; /* Return value of fork() */ - p->thread.s[0] =3D 0; + p->thread.ra =3D (unsigned long)ret_from_fork_user_asm; } p->thread.riscv_v_flags =3D 0; if (has_vector() || has_xtheadvector()) riscv_v_thread_alloc(p); - p->thread.ra =3D (unsigned long)ret_from_fork_asm; p->thread.sp =3D (unsigned long)childregs; /* kernel sp */ return 0; } --=20 2.43.0