From patchwork Wed May 18 10:27:07 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dmitry Konishchev X-Patchwork-Id: 96147 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [140.186.70.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 41255B6F65 for ; Wed, 18 May 2011 20:27:23 +1000 (EST) Received: from localhost ([::1]:60618 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QMdyJ-0006P7-PE for incoming@patchwork.ozlabs.org; Wed, 18 May 2011 06:27:19 -0400 Received: from eggs.gnu.org ([140.186.70.92]:59299) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QMdyB-0006P0-Uc for qemu-devel@nongnu.org; Wed, 18 May 2011 06:27:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QMdyA-0003Nd-Ns for qemu-devel@nongnu.org; Wed, 18 May 2011 06:27:11 -0400 Received: from mail-bw0-f45.google.com ([209.85.214.45]:43836) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QMdyA-0003NQ-H9 for qemu-devel@nongnu.org; Wed, 18 May 2011 06:27:10 -0400 Received: by bwz16 with SMTP id 16so1387972bwz.4 for ; Wed, 18 May 2011 03:27:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:message-id:date:from:user-agent:mime-version:to :cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=oARFBSaU+KtYfqi3/nF2NzEQc0JfgNWgRY97LvQuyiY=; b=n3gx2MkNXaTSMOuyIt7FaryG3kvE8wTn9cV+dCAibL5KfCjqIKWgSFkk6ugJ9rDw0c Sp2IqjUvyZ2KLG8CRmmZm7/3PT6gMkTFDE3t6J2WBWmscb6jNCJNRmHLYmyzXCGt5cQc u/T8XqrcFbp09wzBFk9uJETados+NoqBEgajQ= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; b=D0xczHkiYjbUbzz3vNbisL6nWaCsmpfRmclPTgId621mWBOIY53l5HDQrF3PQNpp56 WQWnWZQaQBsBntG90aWUTEc4q3vc2nE3vtWOKSe5KA6ZdTew672kLwDDzny/fRuVX1Nd y4b7GLw4vTGz6hsZwM2SUSKYPfeCTjO4hfmSY= Received: by 10.204.84.27 with SMTP id h27mr1672843bkl.158.1305714429361; Wed, 18 May 2011 03:27:09 -0700 (PDT) Received: from [10.100.43.13] ([94.79.45.97]) by mx.google.com with ESMTPS id u15sm877034bkf.16.2011.05.18.03.27.08 (version=SSLv3 cipher=OTHER); Wed, 18 May 2011 03:27:09 -0700 (PDT) Message-ID: <4DD39EFB.8050400@gmail.com> Date: Wed, 18 May 2011 14:27:07 +0400 From: Dmitry Konishchev User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Thunderbird/3.1.10 MIME-Version: 1.0 To: Kevin Wolf References: <4DD38F03.7020209@gmail.com> <4DD391FC.6070101@redhat.com> In-Reply-To: <4DD391FC.6070101@redhat.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6 (newer, 2) X-Received-From: 209.85.214.45 Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, stanislav.ievlev@gmail.com Subject: Re: [Qemu-devel] [PATCH] [qemu-img] CPU consuming optimization X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org On 18.05.2011 13:31, Kevin Wolf wrote: > Please move the declarations to the start of the function. > > I also would use a single line like "long d0, d1, d2, d3;", but that's > up to you. > >> + >> + for(i = 0; i< len; i += 4) { >> + d0 = ((const long*) sector)[i + 0]; >> + d1 = ((const long*) sector)[i + 1]; >> + d2 = ((const long*) sector)[i + 2]; >> + d3 = ((const long*) sector)[i + 3]; > > I would suggest to declare a const long* variable so that you don't have > to cast each time you use, but that's probably a matter of taste. > >> + >> + if (d0 || d1 || d2 || d3) >> return 1; > > Coding style requires braces here. > >> } >> + >> return 0; >> } OK, fixed. Signed-off-by: Dmitry Konishchev --- qemu-img.c | 29 ++++++++++++++++++++++++++--- 1 files changed, 26 insertions(+), 3 deletions(-) diff --git a/qemu-img.c b/qemu-img.c index e825123..c849c6f 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -496,14 +496,37 @@ static int img_commit(int argc, char **argv) return 0; } +/* + * Checks whether the sector is not a zero sector. + * + * Attention! The len must be a multiple of 4 * sizeof(long) due to + * restriction of optimizations in this function. + */ static int is_not_zero(const uint8_t *sector, int len) { + /* + * Use long as the biggest available internal data type that fits into the + * CPU register and unroll the loop to smooth out the effect of memory + * latency. + */ + int i; - len >>= 2; - for(i = 0;i < len; i++) { - if (((uint32_t *)sector)[i] != 0) + long d0, d1, d2, d3; + const long * const data = (const long *) sector; + + len /= sizeof(long); + + for(i = 0; i < len; i += 4) { + d0 = data[i + 0]; + d1 = data[i + 1]; + d2 = data[i + 2]; + d3 = data[i + 3]; + + if (d0 || d1 || d2 || d3) { return 1; + } } + return 0; }