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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 9ABA3C43219 for ; Mon, 29 Apr 2019 11:44:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6710420673 for ; Mon, 29 Apr 2019 11:44:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728047AbfD2LoT (ORCPT ); Mon, 29 Apr 2019 07:44:19 -0400 Received: from verein.lst.de ([213.95.11.211]:37997 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727933AbfD2LoS (ORCPT ); Mon, 29 Apr 2019 07:44:18 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id 405C268AFE; Mon, 29 Apr 2019 13:44:01 +0200 (CEST) Date: Mon, 29 Apr 2019 13:44:01 +0200 From: Christoph Hellwig To: Robin Murphy Cc: Lu Baolu , Christoph Hellwig , David Woodhouse , Joerg Roedel , ashok.raj@intel.com, jacob.jun.pan@intel.com, alan.cox@intel.com, kevin.tian@intel.com, mika.westerberg@linux.intel.com, pengfei.xu@intel.com, Konrad Rzeszutek Wilk , Marek Szyprowski , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 02/10] swiotlb: Factor out slot allocation and free Message-ID: <20190429114401.GA30333@lst.de> References: <20190421011719.14909-3-baolu.lu@linux.intel.com> <20190422164555.GA31181@lst.de> <0c6e5983-312b-0d6b-92f5-64861cd6804d@linux.intel.com> <20190423061232.GB12762@lst.de> <20190424144532.GA21480@lst.de> <20190426150433.GA19930@lst.de> <93b3d627-782d-cae0-2175-77a5a8b3fe6e@linux.intel.com> <90182d27-5764-7676-8ca6-b2773a40cfe1@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <90182d27-5764-7676-8ca6-b2773a40cfe1@arm.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 29, 2019 at 12:06:52PM +0100, Robin Murphy wrote: > > From the reply up-thread I guess you're trying to include an optimisation > to only copy the head and tail of the buffer if it spans multiple pages, > and directly map the ones in the middle, but AFAICS that's going to tie you > to also using strict mode for TLB maintenance, which may not be a win > overall depending on the balance between invalidation bandwidth vs. memcpy > bandwidth. At least if we use standard SWIOTLB logic to always copy the > whole thing, we should be able to release the bounce pages via the flush > queue to allow 'safe' lazy unmaps. Oh. The head and tail optimization is what I missed. Yes, for that we'd need the offset. > Either way I think it would be worth just implementing the straightforward > version first, then coming back to consider optimisations later. Agreed, let's start simple. Especially as large DMA mappings or allocations should usually be properly aligned anyway, and if not we should fix that for multiple reasons.