From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2A623D111A8 for ; Mon, 1 Dec 2025 10:14:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=C//JOKMQQVhq74SdcbEm6r0tZ93bnR7w3Mc5YX+hJxg=; b=3n9kwl23x0Qg5vweb1Z1Y82lgr lrnxLdgjBDSYOG0MN3yTzElG3UfaxbUaYeexEqP1Dk134xuz2t6cPMsUyVFdo1PzTXczQm9lG+q4K WaBkO7MZHrbcJCCbXsxlWWl+mNpsuUBRCy8AR9+374nwK+a7O8EUJRgsCz1rS0HHKld0WYqx1Yurf vRnYcDtWsymXbR5HaWCJntUVhwqfMNawNChKGi8LfUNeuS8TTfHOqtELp1ZZ1VfXqH5Y3OS49t5zA uW/sE6/Cyg2HB7j/8flNmwsc7OowAwBQXsWK5qP5Q/ZPiqKH8fkRVMUlfm/tjqcAhAexNRX1rA8t0 tRpWL1ig==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vQ0uw-00000003IXa-3QDI; Mon, 01 Dec 2025 10:14:02 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vQ0uu-00000003IWu-1jvu for linux-arm-kernel@lists.infradead.org; Mon, 01 Dec 2025 10:14:01 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 40082497; Mon, 1 Dec 2025 02:13:52 -0800 (PST) Received: from J2N7QTR9R3 (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 403413F73B; Mon, 1 Dec 2025 02:13:57 -0800 (PST) Date: Mon, 1 Dec 2025 10:13:54 +0000 From: Mark Rutland 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, ldv@strace.io, 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: 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-20251201_021400_569423_BD9925AB X-CRM114-Status: GOOD ( 17.96 ) 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> It's probably worth noting that __audit_syscall_entry() only takes 4 syscall arguments, and hence the compiler has elided the copy of regs->regs[4] and regs->regs[5], which it apparently couldn't manage before. > [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]; > } FWIW, I think this is clearer than the 'args++' and the memcpy(), so I'm happy with this regardless of the performance concern. However, as Dmitry says, we should keep this structurally the same as syscall_set_arguments(), and so we should update that in the same way. Mark.