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Levin" To: Jinjie Ruan Cc: linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org, chris@zankel.net, jcmvbkbc@gmail.com, akpm@linux-foundation.org, macro@orcam.me.uk, charlie@rivosinc.com, deller@gmx.de, rostedt@goodmis.org, tglx@linutronix.de, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] arm64: Avoid memcpy() for syscall_get_arguments() Message-ID: <20251127143557.GA2591@strace.io> References: <20251127123630.4149828-1-ruanjinjie@huawei.com> <20251127123630.4149828-3-ruanjinjie@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20251127123630.4149828-3-ruanjinjie@huawei.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251127_063602_248093_4D93E6B0 X-CRM114-Status: GOOD ( 16.39 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Nov 27, 2025 at 08:36:30PM +0800, Jinjie Ruan wrote: > Do not use memcpy() to extract syscall arguments from struct pt_regs > but rather just perform direct assignments. > > The performance benchmarks with Generic Entry patch[1] with audit on > from perf bench basic syscall on kunpeng920 gives roughly a 1% > performance uplift and also aligns the implementation with > x86 and RISC-V. > > | Metric | W/O this patch | With this patch | Change | > | ---------- | -------------- | --------------- | --------- | > | Total time | 2.241 [sec] | 2.211 [sec] | ↓1.36% | > | usecs/op | 0.224157 | 0.221146 | ↓1.36% | > | ops/sec | 4,461,157 | 4,501,409 | ↑0.9% | > > Before: > : > aa0103e2 mov x2, x1 > 91002003 add x3, x0, #0x8 > f9408804 ldr x4, [x0, #272] > f8008444 str x4, [x2], #8 > a9409404 ldp x4, x5, [x0, #8] > a9009424 stp x4, x5, [x1, #8] > a9418400 ldp x0, x1, [x0, #24] > a9010440 stp x0, x1, [x2, #16] > f9401060 ldr x0, [x3, #32] > f9001040 str x0, [x2, #32] > d65f03c0 ret > d503201f nop > > After: > a9408e82 ldp x2, x3, [x20, #8] > 2a1603e0 mov w0, w22 > f9400e84 ldr x4, [x20, #24] > f9408a81 ldr x1, [x20, #272] > 9401c4ba bl ffff800080215ca8 <__audit_syscall_entry> > > [1]: https://lore.kernel.org/all/20251126071446.3234218-1-ruanjinjie@huawei.com/ > Signed-off-by: Jinjie Ruan > --- > arch/arm64/include/asm/syscall.h | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h > index f3853047c28e..f3564ba97f7e 100644 > --- a/arch/arm64/include/asm/syscall.h > +++ b/arch/arm64/include/asm/syscall.h > @@ -82,9 +82,11 @@ static inline void syscall_get_arguments(struct task_struct *task, > unsigned long *args) > { > args[0] = regs->orig_x0; > - args++; > - > - memcpy(args, ®s->regs[1], 5 * sizeof(args[0])); > + args[1] = regs->regs[1]; > + args[2] = regs->regs[2]; > + args[3] = regs->regs[3]; > + args[4] = regs->regs[4]; > + args[5] = regs->regs[5]; > } > > static inline void syscall_set_arguments(struct task_struct *task, Please keep syscall_get_arguments() and syscall_set_arguments() in sync: if you replace memset() with direct assignments in one of these functions, please mirror the change in another. -- ldv