From owner-freebsd-arch@FreeBSD.ORG Mon Jun 2 05:27:57 2008 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 07AA11065676 for ; Mon, 2 Jun 2008 05:27:57 +0000 (UTC) (envelope-from eischen@vigrid.com) Received: from mail.netplex.net (mail.netplex.net [204.213.176.10]) by mx1.freebsd.org (Postfix) with ESMTP id 91E578FC12 for ; Mon, 2 Jun 2008 05:27:56 +0000 (UTC) (envelope-from eischen@vigrid.com) Received: from sea.ntplx.net (sea.ntplx.net [204.213.176.11]) by mail.netplex.net (8.14.3/8.14.3/NETPLEX) with ESMTP id m525RabW009486; Mon, 2 Jun 2008 01:27:36 -0400 (EDT) X-Virus-Scanned: by AMaViS and Clam AntiVirus (mail.netplex.net) X-Greylist: Message whitelisted by DRAC access database, not delayed by milter-greylist-4.0 (mail.netplex.net [204.213.176.10]); Mon, 02 Jun 2008 01:27:36 -0400 (EDT) Date: Mon, 2 Jun 2008 01:27:36 -0400 (EDT) From: Daniel Eischen X-X-Sender: eischen@sea.ntplx.net To: Julian Elischer In-Reply-To: <4843808A.2060501@elischer.org> Message-ID: References: <483EE7D5.5050408@elischer.org> <20080601215759.GN64397@hoeg.nl> <4843808A.2060501@elischer.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Ed Schouten , arch@freebsd.org Subject: Re: all mutexes -> read-write locks? X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 Jun 2008 05:27:57 -0000 On Sun, 1 Jun 2008, Julian Elischer wrote: > Daniel Eischen wrote: >> On Sun, 1 Jun 2008, Ed Schouten wrote: >> >>> Hello Julian, >>> >>> * Julian Elischer wrote: >>>> it has been mentioned several times that through the evolution of the >>>> locking primitives it has come to be that mutexes and exclusively >>>> acquired reader-writer locks are almost the same in terms of overhead >>>> and that it might be a good move to define all mutexes to be >>>> actually just that. >>>> >>>> this would allow people to slowly go through the system, catching low >>>> hanging fruit by converting some of the mutex operations to reader >>>> acquisitions wherever a writer is not required, thus reducing general >>>> system contention. >>>> >>>> Is there any thought on this? Last I heard jhb had confirmed that it >>>> was feasible.. >>> >>> If this is going to be done, could we have mtx_* macro's pointing to the >>> proper read/write ops? I know, it's just names, but I think most novice >>> FreeBSD kernel hackers will almost instantaneously figure out what 'mtx' >>> stands for. >> >> Yes, mutex (mtx) is known very well. >> >> I don't think changing all mutex operations to rdlock operations >> is wise. They are two different animals, regardless of their >> implementation. Mutexes are very commonly used in device drivers, >> at least outside of FreeBSD. And just because our current >> implementation of them are the same as rwlocks doesn't mean that >> it will always be the same in the future. >> > > so let's imagine that mutexes dissappear... > :-) I'd rather not. What do you have against them? Their API is simple enough to use. If there is code that really wants to have multiple readers, by all means change it to use rwlocks. Take a look at Solaris kernel mutexes and see how you can init a mutex that is to be used in an interrupt handler. -- DE