From owner-freebsd-current@FreeBSD.ORG  Fri Jun  5 18:52:46 2015
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id 67344976
 for <freebsd-current@freebsd.org>; Fri,  5 Jun 2015 18:52:46 +0000 (UTC)
 (envelope-from hps@selasky.org)
Received: from mail.turbocat.net (mail.turbocat.net
 [IPv6:2a01:4f8:d16:4514::2])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id 2C88410CA
 for <freebsd-current@freebsd.org>; Fri,  5 Jun 2015 18:52:46 +0000 (UTC)
 (envelope-from hps@selasky.org)
Received: from laptop015.home.selasky.org
 (cm-176.74.213.204.customer.telag.net [176.74.213.204])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (No client certificate requested)
 by mail.turbocat.net (Postfix) with ESMTPSA id 2B3851FE023;
 Fri,  5 Jun 2015 20:52:44 +0200 (CEST)
Message-ID: <5571F02B.4080907@selasky.org>
Date: Fri, 05 Jun 2015 20:53:31 +0200
From: Hans Petter Selasky <hps@selasky.org>
User-Agent: Mozilla/5.0 (X11; FreeBSD amd64;
 rv:31.0) Gecko/20100101 Thunderbird/31.4.0
MIME-Version: 1.0
To: Neel Natu <neelnatu@gmail.com>
CC: FreeBSD Current <freebsd-current@freebsd.org>
Subject: Re: [CFR] Replacing while loops with proper division and
 multiplication
References: <55714B26.6060802@selasky.org>
 <CAFgRE9HOmzv+SuzWjsKDtsgRJCP3LpGJEQmd02_V=35__OE91A@mail.gmail.com>
In-Reply-To: <CAFgRE9HOmzv+SuzWjsKDtsgRJCP3LpGJEQmd02_V=35__OE91A@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.20
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
 <freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-current>, 
 <mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current/>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
 <mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 05 Jun 2015 18:52:46 -0000

On 06/05/15 20:31, Neel Natu wrote:
>>> -       runs = 0;
>>> >>-       while (now >= state->nexthard) {
>>> >>-               state->nexthard += tick_sbt;
>>> >>-               runs++;
>>> >>-       }
>>> >>-       if (runs) {
>>> >>+       runs = (now - state->nexthard) / tick_sbt;
>>> >>+       if (runs > 0) {
>>> >>+               printf("R%d ", (int)runs);
>>> >>+               state->nexthard += tick_sbt * runs;
>>> >>                 hct = DPCPU_PTR(hardclocktime);
>>> >>                 *hct = state->nexthard - tick_sbt;
>>> >>                 if (fake < 2) {
> There is a difference in behavior in the two implementations when 'now
> == state->nexthard'. In the loop-based implementation this would end
> up with 'runs = 1' whereas in the division-based implementation it
> would end up with 'runs = 0'.
>
> I am not sure if this is intentional or just an oversight.

Hi Neel,

The nexthard is mainly updated in this piece of code. We can assume that 
"state->nexthard" is aligned to "ticks_sbt". If "state->nexthard % 
ticks_sbt == 0", is that still an issue?

--HPS