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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 A9E1AC2BA19 for ; Wed, 15 Apr 2020 07:50:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8624520768 for ; Wed, 15 Apr 2020 07:50:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2635342AbgDOHty (ORCPT ); Wed, 15 Apr 2020 03:49:54 -0400 Received: from smtprelay0207.hostedemail.com ([216.40.44.207]:45180 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2635311AbgDOHtx (ORCPT ); Wed, 15 Apr 2020 03:49:53 -0400 Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay06.hostedemail.com (Postfix) with ESMTP id F013918015D9D; Wed, 15 Apr 2020 07:49:51 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: juice76_900e1bed61f58 X-Filterd-Recvd-Size: 2008 Received: from XPS-9350.home (unknown [47.151.136.130]) (Authenticated sender: joe@perches.com) by omf12.hostedemail.com (Postfix) with ESMTPA; Wed, 15 Apr 2020 07:49:49 +0000 (UTC) Message-ID: Subject: Re: [PATCH] Bitmap: Optimized division operation to shift operation From: Joe Perches To: Wang Qing , Andrew Morton , Dennis Zhou , Wolfram Sang , David Sterba , Josef Bacik , Stefano Brivio , Thomas Gleixner , William Breathitt Gray , Randy Dunlap , Andy Shevchenko , Yury Norov , linux-kernel@vger.kernel.org Cc: opensource.kernel@vivo.com Date: Wed, 15 Apr 2020 00:47:39 -0700 In-Reply-To: <1586935667-4792-1-git-send-email-wangqing@vivo.com> References: <1586935667-4792-1-git-send-email-wangqing@vivo.com> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.34.1-2 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2020-04-15 at 15:27 +0800, Wang Qing wrote: > On some processors, the / operate will call the compiler`s div lib, > which is low efficient. Bitmap is performance sensitive, We can > replace the / operation with shift. Seems more like bad compilers than useful code changes unless you can specify what compilers and what processors. > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h [] > @@ -337,7 +337,7 @@ static inline int bitmap_equal(const unsigned long *src1, > return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); > if (__builtin_constant_p(nbits & BITMAP_MEM_MASK) && > IS_ALIGNED(nbits, BITMAP_MEM_ALIGNMENT)) > - return !memcmp(src1, src2, nbits / 8); > + return !memcmp(src1, src2, nbits >> 3);