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=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 A5189C2BA19 for ; Wed, 15 Apr 2020 08:57:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 81EE120737 for ; Wed, 15 Apr 2020 08:57:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pWNb6KFc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408197AbgDOI5Y (ORCPT ); Wed, 15 Apr 2020 04:57:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43602 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S2405268AbgDOI5I (ORCPT ); Wed, 15 Apr 2020 04:57:08 -0400 Received: from merlin.infradead.org (unknown [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 86CBAC061A0C for ; Wed, 15 Apr 2020 01:57:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Z18reNrEyKf1NJjD06HCmDGv5FbGXihQe6KKOmGQo/8=; b=pWNb6KFcsYvhPeAtMzL5R6dC4I 3wiihazVHIuDUhC1XjYwc2/uTrREiYD1Sfn31kF1RN0LsOC7kGY+ociNXGEJqKw6AUCC5DHw66HI0 bfI+wqBZf/SW/b55o4UuLKqkkElh5iu51rSsKnmcNR5aATmPpvMXWb7x4zvWKev+c8bpdcnzLdfzl ublnKKEpvOKq2iP6c5b7pCCm87PIJmR0mAc1gGUPlTFsacHElIALdEqMGBfeTBNrQASOx4Gi9PYJO s2CMwwP9i1bQWSfg+NVd8T6FOc1hqYzF2mRSDrBfffPQcCGkAgj6B294QDPWkZbXImaGHKHDTFgod 2o11meag==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jOdqX-0004qd-W9; Wed, 15 Apr 2020 08:56:38 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 253A8305EEC; Wed, 15 Apr 2020 10:56:35 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 101EE20B07BFE; Wed, 15 Apr 2020 10:56:35 +0200 (CEST) Date: Wed, 15 Apr 2020 10:56:34 +0200 From: Peter Zijlstra To: Wang Qing Cc: 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, opensource.kernel@vivo.com Subject: Re: [PATCH] Bitmap: Optimized division operation to shift operation Message-ID: <20200415085634.GA17091@hirez.programming.kicks-ass.net> References: <1586935667-4792-1-git-send-email-wangqing@vivo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1586935667-4792-1-git-send-email-wangqing@vivo.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 15, 2020 at 03:27:40PM +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. > > Signed-off-by: Wang Qing > --- > include/linux/bitmap.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h > index 99058eb..85ff982 100644 > --- 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); > return __bitmap_equal(src1, src2, nbits); > } If your compiler gets this wrong, set it on fire and scatter its remains.