From owner-svn-src-user@FreeBSD.ORG Wed Oct 24 15:24:23 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 C803B1F0; Wed, 24 Oct 2012 15:24:23 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from mail-vb0-f54.google.com (mail-vb0-f54.google.com [209.85.212.54]) by mx1.freebsd.org (Postfix) with ESMTP id 19D6C8FC0A; Wed, 24 Oct 2012 15:24:23 +0000 (UTC) Received: by mail-vb0-f54.google.com with SMTP id v11so833471vbm.13 for ; Wed, 24 Oct 2012 08:24:22 -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=9ZuwUFsIT6JHjjJFPX9F+KYbaNn40WhrWo2av9DOHR4=; b=a+aYmEWt0TAl5dQLE+jQKzr0pFjtBUk6E0gY6HSDdoXPhQv1Tot2J3JJLEG2ZW9vwo Fkrl2t0V8u3qbb0CWdwsBk/1uImGpFEJt6KK8Nc8ddEU9nwHPSpHWvllRuDM1wGbKBWc WwmGLmZcvhQj1rMqM9kpH961SP5PJqXt+CimIFehl4K4oAwHg2SxW55ndxUjlVgsKsWv Fz9tg6/ugEUWVmFu2di32ew1PDxtoR7/1SbeYdAAWZ0hRmhCZGuMDQk7Tm1XZVDV1/E1 ALVPSWFog2S9+6KsWRZKtvLrGIo4x2/q7ICV+0BK6FUfONQRDwTggAcThuEN+CmJSG4x Ps9A== MIME-Version: 1.0 Received: by 10.221.11.15 with SMTP id pc15mr8542017vcb.70.1351092262606; Wed, 24 Oct 2012 08:24:22 -0700 (PDT) Sender: asmrookie@gmail.com Received: by 10.220.150.197 with HTTP; Wed, 24 Oct 2012 08:24:22 -0700 (PDT) In-Reply-To: References: <201210221418.q9MEINkr026751@svn.freebsd.org> <201210241005.38977.jhb@freebsd.org> <201210241045.39211.jhb@freebsd.org> Date: Wed, 24 Oct 2012 16:24:22 +0100 X-Google-Sender-Auth: _HhjQYkYQqIWXn3WpS3HJFQUStU 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: John Baldwin Content-Type: text/plain; charset=UTF-8 Cc: mdf@freebsd.org, src-committers@freebsd.org, Andre Oppermann , Bruce Evans , 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 15:24:24 -0000 On Wed, Oct 24, 2012 at 4:09 PM, 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. > 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. The quickest way I see this can be made general is to have a specific struct defined in sys/_mutex.h like that struct mtx_unshare { struct mtx lock; char _pad[CACHE_LINE_SIZE - sizeof(struct mtx)]; } __aligned(CACHE_LINE_SIZE); then let mtx_* functions to accept void ptrs and cast them to struct mtx as long as the functions enter. I think that almost all the static/non-member-of-a-struct mutex should be converted to be struct mtx_unshare, or possibly the most coarse-grained ones. Attilio -- Peace can only be achieved by understanding - A. Einstein