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Date: Mon, 7 May 2018 10:04:20 +0200
From: Joerg Roedel <joro@8bytes.org>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
        Thierry Reding <thierry.reding@gmail.com>, linux-tegra@vger.kernel.org,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        Jonathan Hunter <jonathanh@nvidia.com>
Subject: Re: [PATCH v1 4/4] iommu/tegra: gart: Optimize map/unmap
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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