From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BCBEEC433ED for ; Mon, 10 May 2021 15:25:33 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 57F9E61139 for ; Mon, 10 May 2021 15:25:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 57F9E61139 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id AC81C6E4AE; Mon, 10 May 2021 15:25:32 +0000 (UTC) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9F7906E4AB; Mon, 10 May 2021 15:25:28 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id E63D667373; Mon, 10 May 2021 17:25:25 +0200 (CEST) Date: Mon, 10 May 2021 17:25:25 +0200 From: Christoph Hellwig To: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi Message-ID: <20210510152525.GA30093@lst.de> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.17 (2007-11-01) Subject: [Intel-gfx] i915 and swiotlb_max_segment X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-gfx@lists.freedesktop.org, iommu@lists.linux-foundation.org, dri-devel@lists.freedesktop.org, Konrad Rzeszutek Wilk Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Hi all, swiotlb_max_segment is a rather strange "API" export by swiotlb.c, and i915 is the only (remaining) user. swiotlb_max_segment returns 0 if swiotlb is not in use, 1 if SWIOTLB_FORCE is set or swiotlb-zen is set, and the swiotlb segment size when swiotlb is otherwise enabled. i915 then uses it to: a) decided on the max order in i915_gem_object_get_pages_internal b) decide on a max segment size in i915_sg_segment_size for a) it really seems i915 should switch to dma_alloc_noncoherent or dma_alloc_noncontigous ASAP instead of using alloc_page and streaming DMA mappings. Any chance I could trick one of the i915 maintaines into doing just that given that the callchain is not exactly trivial? For b) I'm not sure swiotlb and i915 really agree on the meaning of the value. swiotlb_set_max_segment basically returns the entire size of the swiotlb buffer, while i915 seems to use it to limit the size each scatterlist entry. It seems like dma_max_mapping_size might be the best value to use here. Once that is fixed I'd like to kill off swiotlb_max_segment as it is a horribly confusing API. _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx