From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.kundenserver.de ([212.227.126.130]:49248 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757260AbaEITwu (ORCPT ); Fri, 9 May 2014 15:52:50 -0400 From: Arnd Bergmann To: Bjorn Helgaas Cc: David Woodhouse , linux-doc@vger.kernel.org, Greg Kroah-Hartman , Joerg Roedel , Randy Dunlap , Liviu Dudau , linux-kernel@vger.kernel.org, James Bottomley , linux-pci@vger.kernel.org Subject: Re: [PATCH v2 4/5] iommu: Use dma_addr_t for IOVA arguments Date: Fri, 09 May 2014 21:52:08 +0200 Message-ID: <9450765.GaoRYW154J@wuerfel> In-Reply-To: <20140509153226.GA3571@google.com> References: <20140506223250.17968.27054.stgit@bhelgaas-glaptop.roam.corp.google.com> <1399629530.879.21.camel@i7.infradead.org> <20140509153226.GA3571@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: linux-pci-owner@vger.kernel.org List-ID: On Friday 09 May 2014 09:32:26 Bjorn Helgaas wrote: > > There are people who care deeply about the performance of IOMMU API > > map/unmap. It isn't used *just* for virtual machines any more. See > > drivers/infiniband/hw/usnic/usnic_uiom.c for example. > > Of course we should care about IOMMU API performance. We should also > care about interface consistency, and it seems there's a tradeoff in > this case. I said "relatively" because I expect map/unmap to be less > frequent than read/write operations that use the mapping. I don't > know anything about infiniband, so maybe that assumption is false > there. In most drivers using the streaming DMA API, every mapping is used exactly once. Think of network or block drivers: they rarely send the same data twice to the device, and it usually comes from or goes to some user space buffer. Arnd