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From: Dmitry Osipenko <digetx@gmail.com>
To: Joerg Roedel <joro@8bytes.org>
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
Date: Mon, 7 May 2018 20:38:31 +0300	[thread overview]
Message-ID: <8967e349-3af1-af17-dfa2-187d06dca18c@gmail.com> (raw)
In-Reply-To: <a6e26d17-97ac-d02e-7bf4-f009af1a25dc@gmail.com>

On 07.05.2018 18:51, Dmitry Osipenko wrote:

[snip]

> Secondly, the interesting part is that mapping / unmapping of a contiguous
> allocation (CMA using DMA API) is slower by ~50% then doing it for a sparse
> allocation (get_pages using bare IOMMU API). /I think/ it's a shortcoming of the
> arch/arm/mm/dma-mapping.c, which also suffers from other inflexibilities that
> Thierry faced recently. Though I haven't really tried to figure out what is the
> bottleneck yet and Thierry was going to re-write ARM's dma-mapping
> implementation anyway, I'll take a closer look at this issue a bit later.

Please scratch my accusation of ARM's dma-mapping, it's not the culprit at all.
I completely forgot that in a case of sparse allocation displays framebuffer
IOMMU mapping is "pinned" to the GART and hence it's not getting dynamically
mapped / unmapped during of my testing. I also forgot to set CPU freq governor
to "perfomance", that reduced 50% to 20% of the above perf difference. The rest
of the testing is unaffected, flushing after whole mapping is still much more
efficient than flushing after modification of each page entry. And yet again,
performance of sparse mapping is nearly the same as of contiguous mapping unless
sparse allocation is large and _very_ fragmented.

  reply	other threads:[~2018-05-07 17:38 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-09 20:07 [PATCH v1 0/4] Tegra GART fixes and improvements Dmitry Osipenko
2018-04-09 20:07 ` [PATCH v1 1/4] iommu/tegra: gart: Add debugging facility Dmitry Osipenko
2018-04-27  9:46   ` Thierry Reding
2018-04-09 20:07 ` [PATCH v1 2/4] iommu/tegra: gart: Fix gart_iommu_unmap() Dmitry Osipenko
2018-04-27  9:43   ` Thierry Reding
2018-04-09 20:07 ` [PATCH v1 3/4] iommu/tegra: gart: Constify number of GART pages Dmitry Osipenko
2018-04-27  9:49   ` Thierry Reding
2018-04-09 20:07 ` [PATCH v1 4/4] iommu/tegra: gart: Optimize map/unmap Dmitry Osipenko
2018-04-27 10:02   ` Thierry Reding
2018-04-27 12:01     ` Dmitry Osipenko
2018-04-27 12:36     ` Robin Murphy
2018-05-06 21:19       ` Dmitry Osipenko
2018-05-07  8:04         ` Joerg Roedel
2018-05-07 15:51           ` Dmitry Osipenko
2018-05-07 17:38             ` Dmitry Osipenko [this message]
2018-05-07  7:59     ` Joerg Roedel
2018-05-07 15:46       ` Dmitry Osipenko
2018-05-03 12:52 ` [PATCH v1 0/4] Tegra GART fixes and improvements Joerg Roedel

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