From: Brian Starkey <brian.starkey@arm.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: "Laura Abbott" <labbott@redhat.com>,
devel@driverdev.osuosl.org, "Rom Lemarchand" <romlem@google.com>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Riley Andrews" <riandrews@android.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
"Michal Hocko" <mhocko@kernel.org>,
"linaro-mm-sig@lists.linaro.org" <linaro-mm-sig@lists.linaro.org>,
linux-mm@kvack.org, "Arve Hjønnevåg" <arve@android.com>,
"Mark Brown" <broonie@kernel.org>,
"Benjamin Gaignard" <benjamin.gaignard@linaro.org>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
linux-arm-kernel@lists.infradead.org,
"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>
Subject: Re: [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging
Date: Fri, 10 Mar 2017 14:27:09 +0000 [thread overview]
Message-ID: <20170310142709.GB15945@e106950-lin.cambridge.arm.com> (raw)
In-Reply-To: <2e295c28-04d6-a071-cf16-164d02d679c5@arm.com>
On Fri, Mar 10, 2017 at 11:46:42AM +0000, Robin Murphy wrote:
>On 10/03/17 10:31, Brian Starkey wrote:
>> Hi,
>>
>> On Thu, Mar 09, 2017 at 09:38:49AM -0800, Laura Abbott wrote:
>>> On 03/09/2017 02:00 AM, Benjamin Gaignard wrote:
>>
>> [snip]
>>
>>>>
>>>> For me those patches are going in the right direction.
>>>>
>>>> I still have few questions:
>>>> - since alignment management has been remove from ion-core, should it
>>>> be also removed from ioctl structure ?
>>>
>>> Yes, I think I'm going to go with the suggestion to fixup the ABI
>>> so we don't need the compat layer and as part of that I'm also
>>> dropping the align argument.
>>>
>>
>> Is the only motivation for removing the alignment parameter that
>> no-one got around to using it for something useful yet?
>> The original comment was true - different devices do have different
>> alignment requirements.
>>
>> Better alignment can help SMMUs use larger blocks when mapping,
>> reducing TLB pressure and the chance of a page table walk causing
>> display underruns.
>
>For that use-case, though, alignment alone doesn't necessarily help -
>you need the whole allocation granularity to match your block size (i.e.
>given a 1MB block size, asking for 17KB and getting back 17KB starting
>at a 1MB boundary doesn't help much - that whole 1MB needs to be
>allocated and everyone needs to know it to ensure that the whole lot can
>be mapped safely). Now, whether it's down to the callers or the heap
>implementations to decide and enforce that granularity is another
>question, but provided allocations are at least naturally aligned to
>whatever the granularity is (which is a reasonable assumption to bake
>in) then it's all good.
>
>Robin.
Agreed, alignment alone isn't enough. But lets assume that an app
knows what a "good" granularity is, and always asks for allocation
sizes which are suitably rounded to allow blocks to be used. Currently
it looks like a "standard" ION_HEAP_TYPE_CARVEOUT heap would give me
back just a PAGE_SIZE aligned buffer. So even *if* the caller knows
its desired block size, there's no way for it to get guaranteed better
alignment, which wouldn't be a bad feature to have.
Anyway as Daniel and Rob say, if the interface is designed properly
this kind of extension would be possible later, or you can have a
special heap with a larger granule.
I suppose it makes sense to remove it while there's no-one actually
implementing it, in case an alternate method proves more usable.
-Brian
>
>>
>> -Brian
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
next prev parent reply other threads:[~2017-03-10 14:27 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-02 21:44 [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 01/12] staging: android: ion: Remove dmap_cnt Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 02/12] staging: android: ion: Remove alignment from allocation field Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 03/12] staging: android: ion: Duplicate sg_table Laura Abbott
2017-03-03 8:18 ` Hillf Danton
2017-03-03 18:41 ` Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 04/12] staging: android: ion: Call dma_map_sg for syncing and mapping Laura Abbott
2017-03-03 11:04 ` Dan Carpenter
2017-03-03 11:58 ` Eric Engestrom
2017-03-03 16:37 ` Laurent Pinchart
2017-03-03 18:40 ` Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 05/12] staging: android: ion: Remove page faulting support Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 06/12] staging: android: ion: Remove crufty cache support Laura Abbott
2017-03-03 9:56 ` Daniel Vetter
2017-03-03 16:39 ` Laurent Pinchart
2017-03-03 18:46 ` Laura Abbott
2017-03-06 10:29 ` Daniel Vetter
2017-03-06 17:00 ` Emil Velikov
2017-03-06 19:20 ` Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 07/12] staging: android: ion: Remove old platform support Laura Abbott
2017-03-03 10:31 ` Daniel Vetter
2017-03-02 21:44 ` [RFC PATCH 08/12] cma: Store a name in the cma structure Laura Abbott
2017-03-10 8:53 ` Sumit Semwal
2017-03-17 18:02 ` Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 09/12] cma: Introduce cma_for_each_area Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 10/12] staging: android: ion: Use CMA APIs directly Laura Abbott
2017-03-03 16:41 ` Laurent Pinchart
2017-03-03 18:50 ` Laura Abbott
2017-03-06 10:32 ` Daniel Vetter
2017-03-06 13:43 ` Laurent Pinchart
2017-03-06 15:52 ` Daniel Vetter
2017-03-06 19:14 ` Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 11/12] staging: android: ion: Make Ion heaps selectable Laura Abbott
2017-03-03 10:33 ` Daniel Vetter
2017-03-03 19:10 ` Laura Abbott
2017-03-02 21:44 ` [RFC PATCH 12/12] staging; android: ion: Enumerate all available heaps Laura Abbott
2017-03-03 10:39 ` Daniel Vetter
2017-03-03 10:04 ` [RFC PATCH 00/12] Ion cleanup in preparation for moving out of staging Daniel Vetter
2017-03-03 10:27 ` Daniel Vetter
2017-03-03 12:54 ` Benjamin Gaignard
2017-03-03 16:45 ` Laurent Pinchart
2017-03-03 19:16 ` Laura Abbott
2017-03-06 10:38 ` Daniel Vetter
2017-03-06 15:02 ` Laurent Pinchart
2017-03-06 16:01 ` Daniel Vetter
2017-03-03 13:29 ` Michal Hocko
2017-03-03 17:37 ` Laura Abbott
2017-03-06 7:42 ` Michal Hocko
2017-03-06 10:40 ` Daniel Vetter
2017-03-06 10:58 ` Mark Brown
2017-03-06 16:04 ` Daniel Vetter
2017-03-09 10:00 ` Benjamin Gaignard
2017-03-09 17:38 ` Laura Abbott
2017-03-10 10:31 ` Brian Starkey
2017-03-10 11:46 ` Robin Murphy
2017-03-10 14:27 ` Brian Starkey [this message]
2017-03-10 16:46 ` Laura Abbott
2017-03-10 12:40 ` Daniel Vetter
2017-03-10 13:56 ` Rob Clark
2017-03-12 13:34 ` Benjamin Gaignard
2017-03-12 19:05 ` Daniel Vetter
2017-03-13 21:09 ` Laura Abbott
2017-03-13 21:29 ` Rob Clark
2017-03-13 21:59 ` Laura Abbott
2017-03-14 14:47 ` Benjamin Gaignard
2017-03-14 19:45 ` Laura Abbott
2017-03-14 20:28 ` Nicolas Dufresne
2017-03-13 10:54 ` Brian Starkey
2017-03-13 13:21 ` Mark Brown
2017-03-13 21:45 ` Laura Abbott
2017-03-13 21:29 ` Laura Abbott
2017-03-06 13:34 ` Michal Hocko
2017-03-03 16:25 ` Laurent Pinchart
2017-03-03 19:14 ` Laura Abbott
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