From owner-freebsd-current@FreeBSD.ORG Sun Jul 22 02:14:49 2007 Return-Path: Delivered-To: current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E954B16A419 for ; Sun, 22 Jul 2007 02:14:49 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.freebsd.org (Postfix) with ESMTP id 85C7C13C45E for ; Sun, 22 Jul 2007 02:14:49 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from [192.168.254.15] (ydesk.samsco.home [192.168.254.15]) (authenticated bits=0) by pooker.samsco.org (8.13.8/8.13.8) with ESMTP id l6M2Ehcq081909; Sat, 21 Jul 2007 20:14:44 -0600 (MDT) (envelope-from scottl@samsco.org) Message-ID: <46A2BD94.2030603@samsco.org> Date: Sat, 21 Jul 2007 20:14:44 -0600 From: Scott Long User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US; rv:1.7.7) Gecko/20050416 X-Accept-Language: en-us, en MIME-Version: 1.0 To: John-Mark Gurney References: <09BFF2FA5EAB4A45B6655E151BBDD9030483F161@NT-IRVA-0750.brcm.ad.broadcom.com> <20070718021839.GA37935@cdnetworks.co.kr> <09BFF2FA5EAB4A45B6655E151BBDD9030483F437@NT-IRVA-0750.brcm.ad.broadcom.com> <20070719002218.GA42405@cdnetworks.co.kr> <09BFF2FA5EAB4A45B6655E151BBDD9030483F5D2@NT-IRVA-0750.brcm.ad.broadcom.com> <469EEF02.7000804@samsco.org> <20070722001240.GA1221@funkthat.com> In-Reply-To: <20070722001240.GA1221@funkthat.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-2.0.2 (pooker.samsco.org [192.168.254.1]); Sat, 21 Jul 2007 20:14:44 -0600 (MDT) X-Spam-Status: No, score=-1.4 required=5.5 tests=ALL_TRUSTED autolearn=failed version=3.1.8 X-Spam-Checker-Version: SpamAssassin 3.1.8 (2007-02-13) on pooker.samsco.org Cc: pyunyh@gmail.com, David Christensen , current@freebsd.org Subject: Re: Getting/Forcing Greater than 4KB Buffer Allocations X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 22 Jul 2007 02:14:50 -0000 John-Mark Gurney wrote: > Scott Long wrote this message on Thu, Jul 19, 2007 at 00:56 -0400: > >>1Gb and 10Gb adapters. The question I have is whether this new back-end >>should be accessible directly through yet another bus_dmamap_load_foo >>variant that the drivers need to know specifically about, or indirectly >>and automatically via the existing bus_dmamap_load_foo variants. The >>tradeoff is further API pollution vs the opportunity for even more >>efficiency through no indirect function calls and no cache misses from >>accessing the busdma tag. I don't like API pollution since it makes it >>harder to maintain code, but the opportunity for the best performance >>possible is also appealing. > > > My vote would be to keep the existing api, and add a flag to the tag > to select which backend to use... > The potential is to avoid cache line misses by disregarding the tag entirely. Drew has a prototype that shows a very good improvement from this. The alternative approach requires tag accesses, but can easily select an appropriate back-end automatically. The tag fields can probably be rearranged so that only a single cache line is needed. If it were possible to give a prefetching hint, it would be a moot point, but I don't think that it is in this case. Scott