From owner-svn-src-user@FreeBSD.ORG Wed Oct 24 15:30:34 2012 Return-Path: Delivered-To: svn-src-user@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 6FADB4C7 for ; Wed, 24 Oct 2012 15:30:34 +0000 (UTC) (envelope-from andre@freebsd.org) Received: from c00l3r.networx.ch (c00l3r.networx.ch [62.48.2.2]) by mx1.freebsd.org (Postfix) with ESMTP id C30D48FC21 for ; Wed, 24 Oct 2012 15:30:33 +0000 (UTC) Received: (qmail 33481 invoked from network); 24 Oct 2012 17:08:21 -0000 Received: from c00l3r.networx.ch (HELO [127.0.0.1]) ([62.48.2.2]) (envelope-sender ) by c00l3r.networx.ch (qmail-ldap-1.03) with SMTP for ; 24 Oct 2012 17:08:21 -0000 Message-ID: <5088098D.9070206@freebsd.org> Date: Wed, 24 Oct 2012 17:30:21 +0200 From: Andre Oppermann User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:16.0) Gecko/20121010 Thunderbird/16.0.1 MIME-Version: 1.0 To: attilio@FreeBSD.org Subject: Re: svn commit: r241889 - in user/andre/tcp_workqueue/sys: arm/arm cddl/compat/opensolaris/kern cddl/contrib/opensolaris/uts/common/dtrace cddl/contrib/opensolaris/uts/common/fs/zfs ddb dev/acpica dev/... References: <201210221418.q9MEINkr026751@svn.freebsd.org> <201210241005.38977.jhb@freebsd.org> <201210241045.39211.jhb@freebsd.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: mdf@freebsd.org, src-committers@freebsd.org, Bruce Evans , John Baldwin , svn-src-user@freebsd.org X-BeenThere: svn-src-user@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "SVN commit messages for the experimental " user" src tree" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 24 Oct 2012 15:30:34 -0000 On 24.10.2012 17:09, Attilio Rao wrote: > On Wed, Oct 24, 2012 at 3:45 PM, John Baldwin wrote: >> On Wednesday, October 24, 2012 10:34:34 am Attilio Rao wrote: >>> On Wed, Oct 24, 2012 at 3:05 PM, John Baldwin wrote: >>>> On Tuesday, October 23, 2012 7:20:04 pm Andre Oppermann wrote: >>>>> On 24.10.2012 00:15, mdf@FreeBSD.org wrote: >>>>>> On Tue, Oct 23, 2012 at 7:41 AM, Andre Oppermann >> wrote: >>>>>>> Struct mtx and MTX_SYSINIT always occur as pair next to each other. >>>>>> >>>>>> That doesn't matter. Language basics like variable definitions should >>>>>> not be obscured by macros. It either takes longer to figure out what >>>>>> a variable is (because one needs to look up the definition of the >>>>>> macro) or makes it almost impossible (because now e.g. cscope doesn't >>>>>> know this is a variable definition. >>>>> >>>>> Sigh, cscope doesn't expand macros? >>>>> >>>>> Is there a way to do the cache line alignment in a sane way without >>>>> littering __aligned(CACHE_LINE_SIZE) all over the place? >>>> >>>> I was hoping to do something with an anonymous union or some such like: >>>> >>>> union mtx_aligned { >>>> struct mtx; >>>> char[roundup2(sizeof(struct mtx), CACHE_LINE_SIZE)]; >>>> } >>>> >>>> I don't know if there is a useful way to define an 'aligned mutex' type >>>> that will transparently map to a 'struct mtx', e.g.: >>>> >>>> typedef struct mtx __aligned(CACHE_LINE_SIZE) aligned_mtx_t; >>> >>> Unfortunately that doesn't work as I've verified with alc@ few months ago. >>> The __aligned() attribute only works with structures definition, not >>> objects declaration. >> >> Are you saying that the typedef doesn't (I expect it doesn't), or that this >> doesn't: >> >> struct mtx foo __aligned(CACHE_LINE_SIZE); > > I meant to say that such notation won't address the padding issue > which is as import as the alignment. Infact, for sensitive locks, > having just an aligned object is not really useful if the cacheline > gets shared. As far as I understand __aligned() not only aligns the start of the object but also ensures that is padded on a multiple of the alignment after the object. So explicit padding after it is not necessary. > In the end you will need to use explicit padding or use __aligned in > the struct definition, which cannot be used as a general pattern. -- Andre