From owner-svn-src-user@FreeBSD.ORG Wed Oct 24 15:32:52 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 DD32B629; Wed, 24 Oct 2012 15:32:51 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-vc0-f182.google.com (mail-vc0-f182.google.com [209.85.220.182]) by mx1.freebsd.org (Postfix) with ESMTP id A7A0C8FC0A; Wed, 24 Oct 2012 15:32:50 +0000 (UTC) Received: by mail-vc0-f182.google.com with SMTP id fw7so829779vcb.13 for ; Wed, 24 Oct 2012 08:32:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:reply-to:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type; bh=XiF9Vj4wBr4Vkr12KwVVfEIGHvf+AXq/lUS1KxqT+eQ=; b=RyEtCX1CyDaNQAh1r9nGFJ68t8cr9VVzqEQ+qcLxA1O7OpnApusfgCNfPTuJadx3Lm teEsj7IWMhjruWasWC80dh04Df+I/lfvVs3Cb5EyPvJgAMIPyriYpL9qo7FF7L02v0bs 2A7GDx/0AEq0vUMNU6vhczLVAAa5WyQaJ1D0rOW3oDjwb+2GREpTvN8Nigw3xn/rRe2R x3MJkVWU4QHkiHSMQho+mt2nBNOm4wv8OxYAGQ/pdUMgqz5d8JooBUmFy35OdmCYXB7z 95ice2AsI6S4wFCnp8b3HT1jCC3ftXP49xusqqRGkmcP/Ed6XvY1VQ4ShYk+mCFysed8 26xA== MIME-Version: 1.0 Received: by 10.52.179.231 with SMTP id dj7mr21644955vdc.108.1351092767998; Wed, 24 Oct 2012 08:32:47 -0700 (PDT) Sender: asmrookie@gmail.com Received: by 10.220.150.197 with HTTP; Wed, 24 Oct 2012 08:32:47 -0700 (PDT) In-Reply-To: <5088098D.9070206@freebsd.org> References: <201210221418.q9MEINkr026751@svn.freebsd.org> <201210241005.38977.jhb@freebsd.org> <201210241045.39211.jhb@freebsd.org> <5088098D.9070206@freebsd.org> Date: Wed, 24 Oct 2012 16:32:47 +0100 X-Google-Sender-Auth: ws9Sj4X4pYqdwpeByH7ehfDUXV8 Message-ID: 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/... From: Attilio Rao To: Andre Oppermann Content-Type: text/plain; charset=UTF-8 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 Reply-To: attilio@FreeBSD.org 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 15:32:52 -0000 On Wed, Oct 24, 2012 at 4:30 PM, Andre Oppermann wrote: > 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. As I said it only works if you specify it in the struct definition, otherwise it doesn't work. You can try it yourself. Attilio -- Peace can only be achieved by understanding - A. Einstein