From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 02/11] iommu-api: Add iommu_map and iommu_unmap functions Date: Sun, 07 Feb 2010 12:52:44 +0200 Message-ID: <4B6E9B7C.3030805@redhat.com> References: <1264678682-30655-1-git-send-email-joerg.roedel@amd.com> <1264678682-30655-3-git-send-email-joerg.roedel@amd.com> <4B6E8A16.8050109@redhat.com> <20100207105007.GC17809@8bytes.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Joerg Roedel , Marcelo Tosatti , David Woodhouse , kvm@vger.kernel.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org To: Joerg Roedel Return-path: In-Reply-To: <20100207105007.GC17809@8bytes.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 02/07/2010 12:50 PM, Joerg Roedel wrote: > On Sun, Feb 07, 2010 at 11:38:30AM +0200, Avi Kivity wrote: > >> On 01/28/2010 01:37 PM, Joerg Roedel wrote: >> >>> These two functions provide support for mapping and >>> unmapping physical addresses to io virtual addresses. The >>> difference to the iommu_(un)map_range() is that the new >>> functions take a gfp_order parameter instead of a size. This >>> allows the IOMMU backend implementations to detect easier if >>> a given range can be mapped by larger page sizes. >>> These new functions should replace the old ones in the long >>> term. >>> >>> >> These seem to be less flexible in the long term. Sure, it is easier for >> the backend to map to multiple page sizes if your iommu supports >> arbitrary power-of-two page sizes, but we should make the APIs easier >> for the callers, not the backend. >> > These functions are as flexible as the old ones which just tok a size. > The benefit of the new interface is that is makes the ability of the > IOMMU to map the area with a large page (an get the benefit of fewer > hardware tlb walks) visible to the caller. With the old interface the > caller is tempted to just map ist whole area using 4kb page sizes. > It gives a bit more complexity to the caller, thats right. But given > that the page allocator in Linux always returns pages which are aligned > to its size takes a lot of that complexity away. > > You are right - I was thinking of the kvm use case which is range oriented, but the ordinary kernel interfaces are gfp_order oriented. -- error compiling committee.c: too many arguments to function