From owner-freebsd-arch@FreeBSD.ORG Wed May 13 14:27:28 2009 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id EC3831065675 for ; Wed, 13 May 2009 14:27:28 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id BF7CE8FC1C for ; Wed, 13 May 2009 14:27:28 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id 7526C46B52; Wed, 13 May 2009 10:27:28 -0400 (EDT) Received: from jhbbsd.hudson-trading.com (unknown [209.249.190.8]) by bigwig.baldwin.cx (Postfix) with ESMTPA id 358738A025; Wed, 13 May 2009 10:27:27 -0400 (EDT) From: John Baldwin To: freebsd-arch@freebsd.org Date: Wed, 13 May 2009 09:35:42 -0400 User-Agent: KMail/1.9.7 References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200905130935.42795.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (bigwig.baldwin.cx); Wed, 13 May 2009 10:27:27 -0400 (EDT) X-Virus-Scanned: clamav-milter 0.95 at bigwig.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-2.5 required=4.2 tests=AWL,BAYES_00,RDNS_NONE autolearn=no version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on bigwig.baldwin.cx Cc: Subject: Re: lockless file descriptor lookup 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: Wed, 13 May 2009 14:27:29 -0000 On Monday 11 May 2009 11:32:17 pm Jeff Roberson wrote: > http://people.freebsd.org/~jeff/locklessfd.diff > > This patch implements a lockless lookup path for file descriptors. The > meat of the algorithm is in fget_unlocked(). This returns a referenced > file descriptor, unlike fget_locked(). In the common case this reduces > the number of atomics required for fget() while allowing for lookups to > proceed concurrently with modifications to the table and preventing > preemption from causing context switches. Looks good. My only comment would be to not remove the 'hold' comment completely from _fget(), but instead say that it always returns a refcount that must be dropped. Basically: * The file's refcount will be bumped on return. It should be dropped * with fdrop(). or something like that in place of the old paragraph about the 'hold' parameter. -- John Baldwin