From owner-freebsd-arch@FreeBSD.ORG Sat Oct 25 19:04:10 2014 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 2274D9C1 for ; Sat, 25 Oct 2014 19:04:10 +0000 (UTC) Received: from h2.funkthat.com (gate2.funkthat.com [208.87.223.18]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "funkthat.com", Issuer "funkthat.com" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id D3EB9BE5 for ; Sat, 25 Oct 2014 19:04:09 +0000 (UTC) Received: from h2.funkthat.com (localhost [127.0.0.1]) by h2.funkthat.com (8.14.3/8.14.3) with ESMTP id s9PJ47XI030946 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Sat, 25 Oct 2014 12:04:08 -0700 (PDT) (envelope-from jmg@h2.funkthat.com) Received: (from jmg@localhost) by h2.funkthat.com (8.14.3/8.14.3/Submit) id s9PJ47s9030945; Sat, 25 Oct 2014 12:04:07 -0700 (PDT) (envelope-from jmg) Date: Sat, 25 Oct 2014 12:04:07 -0700 From: John-Mark Gurney To: Mateusz Guzik Subject: Re: refcount_release_take_##lock Message-ID: <20141025190407.GU82214@funkthat.com> Mail-Followup-To: Mateusz Guzik , freebsd-arch@freebsd.org References: <20141025184448.GA19066@dft-labs.eu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141025184448.GA19066@dft-labs.eu> User-Agent: Mutt/1.4.2.3i X-Operating-System: FreeBSD 7.2-RELEASE i386 X-PGP-Fingerprint: 54BA 873B 6515 3F10 9E88 9322 9CB1 8F74 6D3F A396 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-TipJar: bitcoin:13Qmb6AeTgQecazTWph4XasEsP7nGRbAPE X-to-the-FBI-CIA-and-NSA: HI! HOW YA DOIN? can i haz chizburger? X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.2 (h2.funkthat.com [127.0.0.1]); Sat, 25 Oct 2014 12:04:08 -0700 (PDT) Cc: freebsd-arch@freebsd.org X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 25 Oct 2014 19:04:10 -0000 Mateusz Guzik wrote this message on Sat, Oct 25, 2014 at 20:44 +0200: > The following idiom is used here and there: > > int old; > old = obj->ref; > if (old > 1 && atomic_cmpset_int(&obj->ref, old, old -1)) > return; > lock(&something); > if (refcount_release(&obj->ref) == 0) { > unlock(&something); > return; > } > free up > unlock(&something); > > ========== Couldn't this be better written as: if (__predict_false(refcount_release(&obj->ref) == 0)) { lock(&something); if (__predict_true(!obj->ref)) { free up } unlock(&something); } The reason I'm asking is that I changed how IPsec SA ref counting was handled, and used something similar... My code gets rid of a branch, and is better in that it uses refcount API properly, instead of using atomic_cmpset_int... > I decided to implement it as a common function. > > We have only refcount.h and I didn't want to bloat all including code > with additional definitions and as such I came up with a macro that has > to be used in .c file and that will define appropriate inline func. > > I'm definitely looking for better names for REFCOUNT_RELEASE_TAKE_USE_ > macro, assuming it has to stay. You could shorten it to REFCNT_REL_TAKE_ > Comments? Will you update the refcount(9) man page w/ documentation before committing? -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."