From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH v1 4/4] iommu/tegra: gart: Optimize map/unmap Date: Mon, 7 May 2018 10:04:20 +0200 Message-ID: <20180507080420.GB18595@8bytes.org> References: <20180427100202.GO30388@ulmo> <716edf58-38a7-21e5-1668-b866bf392e34@arm.com> <6827bda3-1aa2-da60-a749-8e2dd2e595f3@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <6827bda3-1aa2-da60-a749-8e2dd2e595f3-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Dmitry Osipenko Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Jonathan Hunter , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Thierry Reding , linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: iommu@lists.linux-foundation.org On Mon, May 07, 2018 at 12:19:01AM +0300, Dmitry Osipenko wrote: > Probably the best variant would be to give an explicit control over syncing to a > user of the IOMMU API, like for example device driver may perform multiple > mappings / unmappings and then sync/flush in the end. I'm not sure that it's > really worth the hassle to shuffle the API right now, maybe we can implement it > later if needed. Joerg, do you have objections to a 'compound page' approach? Have you measured the performance difference on both variants? The compound-page approach only works for cases when the physical memory you map contiguous and correctly aligned. If it is really needed I would prefer a separate iotlb_sync_map() call-back that is just NULL when not needed. This way all users that don't need it only get a minimal penalty in the mapping path and you don't have any requirements on the physical memory you map to get good performance. Joerg