From patchwork Thu May 20 09:22:37 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 444375 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78A76C43461 for ; Thu, 20 May 2021 10:11:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6331461D97 for ; Thu, 20 May 2021 10:11:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235937AbhETKNN (ORCPT ); Thu, 20 May 2021 06:13:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:46058 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235231AbhETKLN (ORCPT ); Thu, 20 May 2021 06:11:13 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id C4BAE61963; Thu, 20 May 2021 09:43:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1621503807; bh=MW3yIXAfcBoXXRXxaYwi0JgwfVDxofXfnrb2vjB8MxQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GvQ5ZKYsLmYWT+L04rXGFS+7Q2lhAgGUHs3NusG2Uxb7Xl45mDUthnL9Ysq0+CBRS GaGv2tPlzeMuTFA9RvgpXBi+CxntF+4/V8leqY6P6RyUP4SOsXPFW43qwLoiH159aE SQ09KtqkS79ds4iqhCrfMN46Auahmfhm4Y0X/PAs= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Maciej W. Rozycki" , Thomas Bogendoerfer Subject: [PATCH 4.19 388/425] MIPS: Avoid handcoded DIVU in `__div64_32 altogether Date: Thu, 20 May 2021 11:22:37 +0200 Message-Id: <20210520092144.154576668@linuxfoundation.org> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210520092131.308959589@linuxfoundation.org> References: <20210520092131.308959589@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Maciej W. Rozycki commit 25ab14cbe9d1b66fda44c71a2db7582a31b6f5cd upstream. Remove the inline asm with a DIVU instruction from `__div64_32' and use plain C code for the intended DIVMOD calculation instead. GCC is smart enough to know that both the quotient and the remainder are calculated with single DIVU, so with ISAs up to R5 the same instruction is actually produced with overall similar code. For R6 compiled code will work, but separate DIVU and MODU instructions will be produced, which are also interlocked, so scalar implementations will likely not perform as well as older ISAs with their asynchronous MD unit. Likely still faster then the generic algorithm though. This removes a compilation error for R6 however where the original DIVU instruction is not supported anymore and the MDU accumulator registers have been removed and consequently GCC complains as to a constraint it cannot find a register for: In file included from ./include/linux/math.h:5, from ./include/linux/kernel.h:13, from mm/page-writeback.c:15: ./include/linux/math64.h: In function 'div_u64_rem': ./arch/mips/include/asm/div64.h:76:17: error: inconsistent operand constraints in an 'asm' 76 | __asm__("divu $0, %z1, %z2" \ | ^~~~~~~ ./include/asm-generic/div64.h:245:25: note: in expansion of macro '__div64_32' 245 | __rem = __div64_32(&(n), __base); \ | ^~~~~~~~~~ ./include/linux/math64.h:91:22: note: in expansion of macro 'do_div' 91 | *remainder = do_div(dividend, divisor); | ^~~~~~ This has passed correctness verification with test_div64 and reduced the module's average execution time down to 1.0404s from 1.0445s with R3400 @40MHz. The module's MIPS I machine code has also shrunk by 12 bytes or 3 instructions. Signed-off-by: Maciej W. Rozycki Signed-off-by: Thomas Bogendoerfer Signed-off-by: Greg Kroah-Hartman --- arch/mips/include/asm/div64.h | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) --- a/arch/mips/include/asm/div64.h +++ b/arch/mips/include/asm/div64.h @@ -58,7 +58,6 @@ #define __div64_32(n, base) ({ \ unsigned long __upper, __low, __high, __radix; \ - unsigned long long __modquot; \ unsigned long long __quot; \ unsigned long long __div; \ unsigned long __mod; \ @@ -73,11 +72,8 @@ __upper = __high; \ __high = 0; \ } else { \ - __asm__("divu $0, %z1, %z2" \ - : "=x" (__modquot) \ - : "Jr" (__high), "Jr" (__radix)); \ - __upper = __modquot >> 32; \ - __high = __modquot; \ + __upper = __high % __radix; \ + __high /= __radix; \ } \ \ __mod = do_div64_32(__low, __upper, __low, __radix); \