Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262134AbVCBA2k (ORCPT ); Tue, 1 Mar 2005 19:28:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262136AbVCBA2k (ORCPT ); Tue, 1 Mar 2005 19:28:40 -0500 Received: from rwcrmhc12.comcast.net ([216.148.227.85]:64720 "EHLO rwcrmhc12.comcast.net") by vger.kernel.org with ESMTP id S262134AbVCBA2h (ORCPT ); Tue, 1 Mar 2005 19:28:37 -0500 Message-ID: <422508A6.9070605@acm.org> Date: Tue, 01 Mar 2005 18:28:22 -0600 From: Corey Minyard User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20040913 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Nick Piggin 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> <42250299.8080709@yahoo.com.au> In-Reply-To: <42250299.8080709@yahoo.com.au> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1552 Lines: 46 Nick Piggin wrote: > 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. It is certainly more complex to use this, and I'm guessing that's why Greg rejected it. Certainly a valid problem. > > 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. True. But if things picked up entries of the queue and incremented their refcount, then you would need a lock. The same technique would apply. But your example would be the more common one, I would think. Thanks, -Corey - 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/