From owner-freebsd-current@FreeBSD.ORG  Sat Aug 24 19:27:44 2013
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115])
 (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTP id 45D8DF43;
 Sat, 24 Aug 2013 19:27:44 +0000 (UTC)
 (envelope-from adrian.chadd@gmail.com)
Received: from mail-we0-x233.google.com (mail-we0-x233.google.com
 [IPv6:2a00:1450:400c:c03::233])
 (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits))
 (No client certificate requested)
 by mx1.freebsd.org (Postfix) with ESMTPS id 7D1402EDF;
 Sat, 24 Aug 2013 19:27:43 +0000 (UTC)
Received: by mail-we0-f179.google.com with SMTP id t58so1550860wes.24
 for <multiple recipients>; Sat, 24 Aug 2013 12:27:41 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113;
 h=mime-version:sender:in-reply-to:references:date:message-id:subject
 :from:to:cc:content-type;
 bh=oASVWtpePHxaRW5wolnyoKaADXSvTcRcQpdhHiMvE9I=;
 b=DZrimS/IHtUbxqDEiswgKnX43Z8AszekQqi6s63ngOhMarTUJqNEbRMJ8i9A76EfrU
 1rvVo16i7MtsIR5ITL2pvd8pA62vQ9w91hlYt8WBwbGbya745WcHCIvpNsHN4gSJ9EEY
 SKIO2fmEOqKEIJJhrh0jIw93StsLXBi//3nYJwaYuDXaDpWV4X/iJQ9LE2DSoH0DHF5S
 7pbqnrs86r6pWBEbvwDjBzuXb4gN5Wsv2rAWAyQEN7EzB7xLV+9rtAgCfpOXUPdDUDHq
 9SuTzbMMWkT3QcX8IsL6Nb8h1bkEUK5Jbg7zpspyxxjllY3+KfKcgaNvfU9Jzbk+7/kH
 yhyw==
MIME-Version: 1.0
X-Received: by 10.180.37.164 with SMTP id z4mr2280515wij.30.1377372461371;
 Sat, 24 Aug 2013 12:27:41 -0700 (PDT)
Sender: adrian.chadd@gmail.com
Received: by 10.217.116.136 with HTTP; Sat, 24 Aug 2013 12:27:41 -0700 (PDT)
In-Reply-To: <E263D234-751F-4948-83CE-48F883F85A59@yahoo.com>
References: <CAJ-Vmo=VKVDEmmPrTbob6Ft+7FWypodNoL36Og=7p_CXBSfktg@mail.gmail.com>
 <5218AA36.1080807@ipfw.ru>
 <alpine.BSF.2.00.1308241511400.92711@fledge.watson.org>
 <5218E108.6090901@mu.org>
 <A4BA90F3-AB8A-41A6-B931-20AF81F903E0@FreeBSD.org>
 <5218F803.7000405@mu.org>
 <E263D234-751F-4948-83CE-48F883F85A59@yahoo.com>
Date: Sat, 24 Aug 2013 12:27:41 -0700
X-Google-Sender-Auth: 8Si-Hdt8VCA9yYgPAARhc5SYsiI
Message-ID: <CAJ-VmomsOkxiQRnYna-=se+ezBy2GajAKBBKCw4p8JiRrmBq3A@mail.gmail.com>
Subject: Re: [rfc] migrate lagg to an rmlock
From: Adrian Chadd <adrian@freebsd.org>
To: Scott Long <scottl@netflix.com>
Content-Type: text/plain; charset=ISO-8859-1
X-Content-Filtered-By: Mailman/MimeDel 2.1.14
Cc: FreeBSD Net <freebsd-net@freebsd.org>, Alfred Perlstein <bright@mu.org>,
 "Robert N. M. Watson" <rwatson@freebsd.org>,
 "Alexander V. Chernikov" <melifaro@ipfw.ru>,
 freebsd-current <freebsd-current@freebsd.org>
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.14
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: Sat, 24 Aug 2013 19:27:44 -0000

Hihi,

There's two parts to my patch:

* one is migrating the rwlock to rmlock - not because of counters, but
because the lock is protecting consistency when changing the lagg config
* one is adding a new lock specifically to ensure that the callout is
atomically created/called/destroyed

The latter has nothing to do with the actual counters - they're already
using the atomic counter API, so the lock doesn't need to be held just to
read them for _counter_ consistency. It's just held to make sure the
callout is never called parallel to the destruction of the lagg interface.



-adrian