Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262133AbVCBACm (ORCPT ); Tue, 1 Mar 2005 19:02:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262127AbVCBACm (ORCPT ); Tue, 1 Mar 2005 19:02:42 -0500 Received: from smtp203.mail.sc5.yahoo.com ([216.136.129.93]:1179 "HELO smtp203.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S262133AbVCBACk (ORCPT ); Tue, 1 Mar 2005 19:02:40 -0500 Message-ID: <42250299.8080709@yahoo.com.au> Date: Wed, 02 Mar 2005 11:02:33 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.5) Gecko/20050105 Debian/1.7.5-1 X-Accept-Language: en MIME-Version: 1.0 To: Corey Minyard CC: Arjan van de Ven , Greg KH , Sergey Vlasov , lkml Subject: Re: [PATCH] New operation for kref to help avoid locks References: <42209BFD.8020908@acm.org> <20050226232026.5c12d5b0.vsu@altlinux.ru> <4220F6C8.4020002@acm.org> <20050301201528.GA23484@kroah.com> <1109710964.6293.166.camel@laptopd505.fenrus.org> <4224E499.5060800@acm.org> <1109715256.6293.180.camel@laptopd505.fenrus.org> <4224FC33.6040405@acm.org> In-Reply-To: <4224FC33.6040405@acm.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1150 Lines: 31 Corey Minyard wrote: > Arjan van de Ven wrote: > >>> Just doing an atomic operation is not faster than doing a lock, an >>> atomic operation, then an unlock? Am I missing something? >>> >> >> >> if the lock and the atomic are on the same cacheline they're the same >> cost on most modern cpus... >> >> > Ah, I see. Not likely to ever be the case with this. The lock will > likely be with the main data structure (the list, or whatever) and the > refcount will be in the individual item in the main data structure (list > entry). > Is get_with_check actually going to be useful for anything? It seems like it promotes complex and potentially unsafe schemes. eg. In your queue example, it would usually be better to have a refcount for being on queue, and entry_completed would remove the entry from the queue and accordingly drop the refcount. The release function would then just free it. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/