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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 189F0C19F2D for ; Tue, 9 Aug 2022 18:55:17 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 018D2C047D; Tue, 9 Aug 2022 18:54:20 +0000 (UTC) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by gabe.freedesktop.org (Postfix) with ESMTPS id 7670214A5FE; Tue, 9 Aug 2022 18:54:07 +0000 (UTC) Received: by verein.lst.de (Postfix, from userid 2407) id A225E68AA6; Tue, 9 Aug 2022 20:54:03 +0200 (CEST) Date: Tue, 9 Aug 2022 20:54:03 +0200 From: "hch@lst.de" To: Tvrtko Ursulin Message-ID: <20220809185403.GB15307@lst.de> References: <20220726153935.2272777-1-bob.beckett@collabora.com> <1160a7c31084ab2259088e4bfe88b41ad61c2bcc.camel@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Subject: Re: [Intel-gfx] [PATCH v5] drm/i915: stop using swiotlb 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: "airlied@linux.ie" , "intel-gfx@lists.freedesktop.org" , "linux-kernel@vger.kernel.org" , "Hellstrom, Thomas" , "dri-devel@lists.freedesktop.org" , "daniel@ffwll.ch" , "Vivi, Rodrigo" , "kernel@collabora.com" , "hch@lst.de" , "Auld, Matthew" Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Tue, Aug 09, 2022 at 12:36:50PM +0100, Tvrtko Ursulin wrote: > > Digging through git history at least running as Xen dom0 looks to have been > impacted, but commits such as abb0deacb5a6 ("drm/i915: Fallback to single > PAGE_SIZE segments for DMA remapping") are older and suggest problem was > generic. 1625e7e549c5 ("drm/i915: make compact dma scatter lists creation > work with SWIOTLB backend.") as well. So it looks it did work behind > swiotlb despite those missing calls you highlighted. Hmm. xen-swiotlb bounce buffers as soon as any single mapping that straddles a Xen page size boundary. Could the magic value there somehow made all mappings small enough to just avoid bounce buffering for Xen by more or less accident?