From owner-freebsd-arch@FreeBSD.ORG Sat Apr 25 18:18:52 2015 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 6A82C806 for ; Sat, 25 Apr 2015 18:18:52 +0000 (UTC) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id D12BB1B5E for ; Sat, 25 Apr 2015 18:18:51 +0000 (UTC) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.14.9/8.14.9) with ESMTP id t3PIIlCj030557 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Sat, 25 Apr 2015 21:18:47 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.9.2 kib.kiev.ua t3PIIlCj030557 Received: (from kostik@localhost) by tom.home (8.14.9/8.14.9/Submit) id t3PIIkiN030556; Sat, 25 Apr 2015 21:18:46 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sat, 25 Apr 2015 21:18:46 +0300 From: Konstantin Belousov To: Jason Harmening Cc: Svatopluk Kraus , FreeBSD Arch Subject: Re: bus_dmamap_sync() for bounced client buffers from user address space Message-ID: <20150425181846.GN2390@kib.kiev.ua> References: <20150425094152.GE2390@kib.kiev.ua> <553B9E64.8030907@gmail.com> <20150425163444.GL2390@kib.kiev.ua> <553BC9D1.1070502@gmail.com> <20150425172833.GM2390@kib.kiev.ua> <553BD501.4010109@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <553BD501.4010109@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.0 X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on tom.home X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.20 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 Apr 2015 18:18:52 -0000 On Sat, Apr 25, 2015 at 12:55:13PM -0500, Jason Harmening wrote: > Ah, that looks much better. A few things though: > 1) _bus_dmamap_load_ma (note the underscore) is still part of the MI/MD > interface, which we tell drivers not to use. It looks like it's > implemented for every arch though. Should there be a public and > documented bus_dmamap_load_ma ? Might be yes. But at least one consumer of the KPI must appear before the facility is introduced. > 2) There is a bus_dmamap_load_ma_triv that's part of the MI interface, > but it's not documented, and it seems like it would be suboptimal in > certain cases, such as when dmar is enabled. When DMAR is enabled, bus_dmamap_load_triv() should not be used. It should not be used directly even when not. Drivers should use bus_dmamap_load_ma(), and implementation redirects to _triv() if needed. The _triv() is the helper to allow bus_dmamap_load_ma() to exists on architectures which cannot implement, on not yet implemented, proper page array load op. > 3) Using bus_dmamap_load_ma would mean always using physcopy for bounce > buffers...seems like the sfbufs would slow things down ? For amd64, sfbufs are nop, due to the direct map. But, I doubt that we can combine bounce buffers and performance in the single sentence.