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 A5B26C76192 for ; Wed, 17 Jul 2019 05:47:36 +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 7CC872173E for ; Wed, 17 Jul 2019 05:47:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7CC872173E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:54218 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hncmt-0000vM-Gz for qemu-devel@archiver.kernel.org; Wed, 17 Jul 2019 01:47:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52184) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hncmZ-0008Lm-TJ for qemu-devel@nongnu.org; Wed, 17 Jul 2019 01:47:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hncmY-0001br-SF for qemu-devel@nongnu.org; Wed, 17 Jul 2019 01:47:15 -0400 Received: from mga11.intel.com ([192.55.52.93]:57666) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hncmY-0001ak-J1 for qemu-devel@nongnu.org; Wed, 17 Jul 2019 01:47:14 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Jul 2019 22:47:13 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,273,1559545200"; d="scan'208";a="191153885" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga004.fm.intel.com with ESMTP; 16 Jul 2019 22:47:12 -0700 Date: Wed, 17 Jul 2019 13:46:47 +0800 From: Wei Yang To: Peter Xu Message-ID: <20190717054647.GA19479@richard> References: <20190717012902.23958-1-richardw.yang@linux.intel.com> <20190717015910.GD30980@xz-x1> <20190717024637.GA17163@richard> <20190717031155.GE30980@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190717031155.GE30980@xz-x1> User-Agent: Mutt/1.9.4 (2018-02-28) X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 192.55.52.93 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: , Reply-To: Wei Yang Cc: quintela@redhat.com, corentincj@iksaif.net, pl@kamp.de, qemu-devel@nongnu.org, kraxel@redhat.com, pbonzini@redhat.com, Wei Yang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 17, 2019 at 11:11:55AM +0800, Peter Xu wrote: >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. Let me have a try. :-) > >At the meantime I think you can also do that to bitmap_set_atomic. > >Thanks, > >-- >Peter Xu -- Wei Yang Help you, Help me