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From: Dmitry Osipenko <digetx@gmail.com>
To: Joerg Roedel <joro@8bytes.org>,
	Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>,
	iommu@lists.linux-foundation.org, linux-tegra@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 4/4] iommu/tegra: gart: Optimize map/unmap
Date: Mon, 7 May 2018 18:46:48 +0300	[thread overview]
Message-ID: <c4cd6692-2010-ec15-f541-b4709932ac82@gmail.com> (raw)
In-Reply-To: <20180507075920.GA18595@8bytes.org>

On 07.05.2018 10:59, Joerg Roedel wrote:
> On Fri, Apr 27, 2018 at 12:02:02PM +0200, Thierry Reding wrote:
>> Joerg, I've gone over the git log and header files and I see no mention
>> of why the TLB flush interface isn't used for mapping. Do you recall any
>> special reasons why the same shouldn't be applied for mapping? Would you
>> accept any patches doing this?
> 
> Yeah, the reason was that we assumed that only emulated IOMMUs ever need
> flushing in the mapping path, and there is no reason to optimize for
> that. Especially when a call to iotlb_sync() in the mapping path would
> hurt most other users.
> 
> Does the tegra-gart actually need it too?

Tegra-GART is exactly an emulated IOMMU, it doesn't have anything like TLB and
it's simply a remapping table. What is actually needed for the GART - is to make
sure that the remapping table modifications reach GART HW before anything tries
to touch the modified page entries. Presumable there is some kind of a HW buffer
that accumulates multiple registers writes and issues them in bursts to improve
performance, read-after-write is the way to flush that buffer.

  reply	other threads:[~2018-05-07 15:46 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
2018-05-07  7:59     ` Joerg Roedel
2018-05-07 15:46       ` Dmitry Osipenko [this message]
2018-05-03 12:52 ` [PATCH v1 0/4] Tegra GART fixes and improvements Joerg Roedel

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