From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joerg Roedel <Joerg.Roedel@amd.com>
Subject: Re: [PATCH v4 2/7] iommu/core: split mapping to page sizes as
 supported by the hardware
Date: Fri, 11 Nov 2011 14:24:11 +0100
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Cc: David Woodhouse <dwmw2@infradead.org>,
	Kai Huang <mail.kai.huang@gmail.com>,
	Ohad Ben-Cohen <ohad@wizery.com>,
	<iommu@lists.linux-foundation.org>, <linux-omap@vger.kernel.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	<linux-arm-kernel@lists.infradead.org>,
	David Brown <davidb@codeaurora.org>,
	Arnd Bergmann <arnd@arndb.de>, <linux-kernel@vger.kernel.org>,
	Hiroshi Doyu <hdoyu@nvidia.com>,
	KyongHo Cho <pullip.cho@samsung.com>, <kvm@vger.kernel.org>
To: Stepan Moskovchenko <stepanm@codeaurora.org>
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On Thu, Nov 10, 2011 at 01:12:00PM -0800, Stepan Moskovchenko wrote:
> I have been experimenting with an iommu_map_range call, which maps a
> given scatterlist of discontiguous physical pages into a contiguous
> virtual region at a given IOVA. This has some performance advantages
> over just calling iommu_map iteratively. First, it reduces the
> amount of table walking / calculation needed for mapping each page,
> given how you know that all the pages will be mapped into a single
> virtually-contiguous region (so in most cases, the first-level table
> calculation can be reused). Second, it allows one to defer the TLB
> (and sometimes cache) maintenance operations until the entire
> scatterlist has been mapped, rather than doing a TLB invalidate
> after mapping each page, as would have been the case if iommu_map
> were just being called from within a loop. Granted, just using
> iommu_map many times may be acceptable on the slow path, but I have
> seen significant performance gains when using this approach on the
> fast path.

Yes, from a performance point-of-view that makes sense, as an addition
to the existing iommu_map interface. Are the pages in the list allowed
to have different page-sizes?


	Joerg

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