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 smtp2.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 064A6C433F5 for ; Fri, 20 May 2022 08:52:04 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp2.osuosl.org (Postfix) with ESMTP id 99F974012F; Fri, 20 May 2022 08:52:04 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ZgGnCGAG5Dc2; Fri, 20 May 2022 08:52:03 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [IPv6:2605:bc80:3010:104::8cd3:938]) by smtp2.osuosl.org (Postfix) with ESMTPS id 6717A40A38; Fri, 20 May 2022 08:52:03 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1A0ACC0032; Fri, 20 May 2022 08:52:03 +0000 (UTC) Received: from smtp1.osuosl.org (smtp1.osuosl.org [IPv6:2605:bc80:3010::138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 999D4C002D for ; Fri, 20 May 2022 08:52:01 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp1.osuosl.org (Postfix) with ESMTP id 76F9E8452D for ; Fri, 20 May 2022 08:52:01 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp1.osuosl.org ([127.0.0.1]) by localhost (smtp1.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id rT96Q61i2rnB for ; Fri, 20 May 2022 08:52:01 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.8.0 Received: from theia.8bytes.org (8bytes.org [IPv6:2a01:238:4383:600:38bc:a715:4b6d:a889]) by smtp1.osuosl.org (Postfix) with ESMTPS id DF8D984526 for ; Fri, 20 May 2022 08:52:00 +0000 (UTC) Received: by theia.8bytes.org (Postfix, from userid 1000) id BC47C1E9; Fri, 20 May 2022 10:51:58 +0200 (CEST) Date: Fri, 20 May 2022 10:51:57 +0200 From: Joerg Roedel To: Christoph Hellwig Subject: Re: [RFC PATCH] dma-iommu: Add iommu_dma_max_mapping_size() Message-ID: References: <1652706361-92557-1-git-send-email-john.garry@huawei.com> <9160031b-50be-6993-5a8e-f238391962c5@huawei.com> <8f193bdd-3a0a-f9ed-0726-e6081f374320@arm.com> <20220518131353.GB26019@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220518131353.GB26019@lst.de> Cc: Robin Murphy , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, will@kernel.org, liyihang6@hisilicon.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, May 18, 2022 at 03:13:53PM +0200, Christoph Hellwig wrote: > On Tue, May 17, 2022 at 01:02:00PM +0100, Robin Murphy wrote: > >> So how to inform the SCSI driver of this caching limit then so that it may > >> limit the SGL length? > > > > Driver-specific mechanism; block-layer-specific mechanism; redefine this > > whole API to something like dma_opt_mapping_size(), as a limit above which > > mappings might become less efficient or start to fail (callback to my > > thoughts on [1] as well, I suppose); many options. Just not imposing a > > ridiculously low *maximum* on everyone wherein mapping calls "should not be > > larger than the returned value" when that's clearly bollocks. > > Well, for swiotlb it is a hard limit. So if we want to go down that > route we need two APIs, one for the optimal size and one for the > hard limit. I agree with Robin, and if it really helps some drivers I am all for doing a dma_opt_mapping_size() instead. Limiting DMA mapping sizes to make drivers perform better gets a clear NAK from my side. Regards, Joerg _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu