From: Tomeu Vizoso <tomeu.vizoso@collabora.com>
To: Steven Price <steven.price@arm.com>,
Rob Herring <robh@kernel.org>,
Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Cc: Neil Armstrong <narmstrong@baylibre.com>,
Robin Murphy <robin.murphy@arm.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
Linux IOMMU <iommu@lists.linux-foundation.org>,
Kevin Hilman <khilman@baylibre.com>,
"open list:ARM/Amlogic Meson..."
<linux-amlogic@lists.infradead.org>,
Will Deacon <will@kernel.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Jerome Brunet <jbrunet@baylibre.com>
Subject: Re: [PATCH 0/3] drm: panfrost: Coherency support
Date: Thu, 17 Sep 2020 12:51:05 +0200 [thread overview]
Message-ID: <0518e067-3b9a-8fe3-619f-8fce4c6c9677@collabora.com> (raw)
In-Reply-To: <d135f546-41aa-a6e2-52fe-7707d379c793@arm.com>
On 9/17/20 12:38 PM, Steven Price wrote:
> On 16/09/2020 18:46, Rob Herring wrote:
>> On Wed, Sep 16, 2020 at 11:04 AM Alyssa Rosenzweig
>> <alyssa.rosenzweig@collabora.com> wrote:
>>>
>>>> So I get a performance regression with the dma-coherent approach,
>>>> even if it's
>>>> clearly the cleaner.
>>>
>>> That's bizarre -- this should really be the faster of the two.
>>
>> Coherency may not be free. CortexA9 had something like 4x slower
>> memcpy if SMP was enabled as an example. I don't know if there's
>> anything going on like that specifically here. If there's never any
>> CPU accesses mixed in with kmscube, then there would be no benefit to
>> coherency.
>
> The DDK blob has the ability to mark only certain areas of memory as
> coherent for performance reasons. For simple things like kmscube I would
> expect that it's basically write-only from the CPU and almost all memory
> the GPU touches isn't touched by the CPU. I.e. coherency isn't helping
> and the coherency traffic is probably expensive. Whether the complexity
> is worth it for "real" content I don't know - it may just be silly
> benchmarks that benefit.
Or maybe it's only a problem for applications that do silly things? I
don't think kmscube was ever optimized for performance.
Regards,
Tomeu
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next prev parent reply other threads:[~2020-09-17 10:52 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 23:51 [PATCH 0/3] drm: panfrost: Coherency support Robin Murphy
2020-09-15 23:51 ` [PATCH 1/3] iommu/io-pgtable-arm: Support coherency for Mali LPAE Robin Murphy
2020-09-21 17:57 ` Will Deacon
2020-09-21 21:53 ` Robin Murphy
2020-09-21 22:24 ` Will Deacon
2020-09-15 23:51 ` [PATCH 2/3] drm/panfrost: Support cache-coherent integrations Robin Murphy
2020-09-17 10:37 ` Steven Price
2020-09-15 23:51 ` [PATCH 3/3] arm64: dts: meson: Describe G12b GPU as coherent Robin Murphy
2020-09-16 8:26 ` Neil Armstrong
2020-10-05 8:15 ` Boris Brezillon
2020-10-05 8:34 ` Steven Price
2020-10-05 8:39 ` Boris Brezillon
2020-10-05 10:05 ` Steven Price
2020-09-16 14:54 ` Neil Armstrong
2020-09-16 14:54 ` [PATCH 0/3] drm: panfrost: Coherency support Neil Armstrong
2020-09-16 17:04 ` Alyssa Rosenzweig
2020-09-16 17:46 ` Rob Herring
2020-09-17 10:38 ` Steven Price
2020-09-17 10:51 ` Tomeu Vizoso [this message]
2020-09-17 11:00 ` Steven Price
2020-09-17 12:03 ` Alyssa Rosenzweig
2020-09-17 12:38 ` Robin Murphy
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