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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 58D27C76188 for ; Wed, 17 Jul 2019 03:12:20 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 217A620818 for ; Wed, 17 Jul 2019 03:12:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 217A620818 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:53772 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnaMd-0005wC-0q for qemu-devel@archiver.kernel.org; Tue, 16 Jul 2019 23:12:19 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35084) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnaMS-0005YE-4i for qemu-devel@nongnu.org; Tue, 16 Jul 2019 23:12:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hnaMR-00006e-2i for qemu-devel@nongnu.org; Tue, 16 Jul 2019 23:12:08 -0400 Received: from mail-pf1-f193.google.com ([209.85.210.193]:40368) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1hnaMQ-00005j-T2 for qemu-devel@nongnu.org; Tue, 16 Jul 2019 23:12:07 -0400 Received: by mail-pf1-f193.google.com with SMTP id p184so10081726pfp.7 for ; Tue, 16 Jul 2019 20:12:06 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=5Cd+K10dF34Ps2D3ey6/NErbheXXyFs+WcBqcQkI4h0=; b=GhXERuHtxNpRPT1Nu57uxPaBWNVqRqO/I2+h3V20dwP/7DxBPtBsJpZKJH84XkwhnE J6kpkiqYHmF1NaQTF5umadjSgjKN7Vx7EqR3BJZ1TDz3eOTYgno+8wFq1kZeFJ15eOv2 jmXH7JFdRxDxNI1ACTYy8ozVmAJ4pZkC40PzYSOgfJe5ovWkyRUZOVYcIS3SLUcfZiXX w8z6kC/0irNWmP18G0zX4hZat3BXIx+BbH2EUm9MyOYB1G+CxxXIeyHVZVXc7m3UvoBR /J8q3B5M2i3/pqP1LDzLbXKb7UVmDM+x9ywyRSwSCn3WPEHPpGByDI9AgBSxVvEiZZsF Rr/g== X-Gm-Message-State: APjAAAXlh86cETeODDIZFaHu0rkBQ0UFmhAC85N791nPDpIhN5hnomqk UCexpZnPOfHOwZxoDxpBnwNrMA== X-Google-Smtp-Source: APXvYqyK85Ihxnmib2nJCHXzkKfXeG3GEvxEamg7cYTSWw2NrnWdAMzZwPdqeCQSsrJLYcMgGoQHLA== X-Received: by 2002:a63:ab08:: with SMTP id p8mr39177708pgf.340.1563333125924; Tue, 16 Jul 2019 20:12:05 -0700 (PDT) Received: from xz-x1 ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id v27sm29230764pgn.76.2019.07.16.20.12.02 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Tue, 16 Jul 2019 20:12:05 -0700 (PDT) From: Peter Xu X-Google-Original-From: Peter Xu Date: Wed, 17 Jul 2019 11:11:55 +0800 To: Wei Yang Message-ID: <20190717031155.GE30980@xz-x1> References: <20190717012902.23958-1-richardw.yang@linux.intel.com> <20190717015910.GD30980@xz-x1> <20190717024637.GA17163@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190717024637.GA17163@richard> User-Agent: Mutt/1.11.4 (2019-03-13) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.85.210.193 Subject: Re: [Qemu-devel] [RESEND][PATCH] bitmap: get last word mask from nr directly X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: quintela@redhat.com, corentincj@iksaif.net, pl@kamp.de, qemu-devel@nongnu.org, Peter Xu , kraxel@redhat.com, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 17, 2019 at 10:46:37AM +0800, Wei Yang wrote: > On Wed, Jul 17, 2019 at 09:59:10AM +0800, Peter Xu wrote: > >On Wed, Jul 17, 2019 at 09:29:02AM +0800, Wei Yang wrote: > >> The value left in nr is the number of bits for the last word, which > >> could be calculate the last word mask directly. > > > >Is it true even if start does not align to BITS_PER_LONG? > > > > Yes. Let me see how to explain this. > > When you look into the definition of BITMAP_LAST_WORD_MASK, it takes the > number of total bits and give the number of bits in last word. While the value > matters for the input is the number of last word. This means the following > equation stands > > BITMAP_LAST_WORD_MASK(size) == BITMAP_FIRST_WORD_MASK(size % BITS_PER_LONG) > > Now let look at the calculation for nr. In each iteration, nr will be > truncated to be aligned to BITS_PER_LONG. So when we exit the loop, nr keeps > the number of bits in last word. > > So we can leverage the result, no matter the start is aligned or not. Yes, you are right. Do you have plan to write some unit tests for these functions? :) It'll be tests/test-bitmap.c. IMHO the test cases could be even more helpful to the QEMU project as a whole comparing to this patch to guarantee changes like your patch won't break. At the meantime I think you can also do that to bitmap_set_atomic. Thanks, -- Peter Xu