From: Tomasz Fujak <t.fujak@samsung.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Michal Nazarewicz <mina86@mina86.com>,
Kyungmin Park <kmpark@infradead.org>,
linux-arm-kernel@lists.infradead.org,
Daniel Walker <dwalker@codeaurora.org>,
Johan MOSSBERG <johan.xx.mossberg@stericsson.com>,
Mel Gorman <mel@csn.ul.ie>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Ankita Garg <ankita@in.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-media@vger.kernel.org,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [PATCHv8 00/12] Contiguous Memory Allocator
Date: Thu, 23 Dec 2010 15:08:21 +0100 [thread overview]
Message-ID: <4D1357D5.9000507@samsung.com> (raw)
In-Reply-To: <20101223135120.GL3636@n2100.arm.linux.org.uk>
On 2010-12-23 14:51, Russell King - ARM Linux wrote:
> On Thu, Dec 23, 2010 at 02:41:26PM +0100, Michal Nazarewicz wrote:
>> Russell King - ARM Linux <linux@arm.linux.org.uk> writes:
>>> Has anyone addressed my issue with it that this is wide-open for
>>> abuse by allocating large chunks of memory, and then remapping
>>> them in some way with different attributes, thereby violating the
>>> ARM architecture specification?
>>>
>>> In other words, do we _actually_ have a use for this which doesn't
>>> involve doing something like allocating 32MB of memory from it,
>>> remapping it so that it's DMA coherent, and then performing DMA
>>> on the resulting buffer?
>> Huge pages.
>>
>> Also, don't treat it as coherent memory and just flush/clear/invalidate
>> cache before and after each DMA transaction. I never understood what's
>> wrong with that approach.
> If you've ever used an ARM system with a VIVT cache, you'll know what's
> wrong with this approach.
>
> ARM systems with VIVT caches have extremely poor task switching
> performance because they flush the entire data cache at every task switch
> - to the extent that it makes system performance drop dramatically when
> they become loaded.
>
> Doing that for every DMA operation will kill the advantage we've gained
> from having VIPT caches and ASIDs stone dead.
This statement effectively means: don't map dma-able memory to the CPU
unless it's uncached. Have I missed anything?
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next prev parent reply other threads:[~2010-12-23 14:08 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-15 20:34 Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 01/12] mm: migrate.c: fix compilation error Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 02/12] lib: bitmap: Added alignment offset for bitmap_find_next_zero_area() Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 03/12] lib: genalloc: Generic allocator improvements Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 04/12] mm: move some functions from memory_hotplug.c to page_isolation.c Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 05/12] mm: alloc_contig_freed_pages() added Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 06/12] mm: alloc_contig_range() added Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 07/12] mm: cma: Contiguous Memory Allocator added Michal Nazarewicz
2011-02-02 12:43 ` Ankita Garg
2011-02-02 14:58 ` Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 08/12] mm: MIGRATE_CMA migration type added Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 09/12] mm: MIGRATE_CMA isolation functions added Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 10/12] mm: MIGRATE_CMA support added to CMA Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 11/12] mm: cma: Test device and application added Michal Nazarewicz
2010-12-15 20:34 ` [PATCHv8 12/12] ARM: cma: Added CMA to Aquila, Goni and c210 universal boards Michal Nazarewicz
2010-12-23 9:30 ` [PATCHv8 00/12] Contiguous Memory Allocator Kyungmin Park
2010-12-23 10:06 ` Russell King - ARM Linux
2010-12-23 10:58 ` Marek Szyprowski
2010-12-23 12:19 ` Russell King - ARM Linux
2010-12-23 13:09 ` Marek Szyprowski
2010-12-23 13:44 ` Russell King - ARM Linux
2011-01-12 18:49 ` Marek Szyprowski
2011-01-12 19:04 ` Nicolas Pitre
2011-01-13 7:01 ` Marek Szyprowski
2010-12-23 13:35 ` Tomasz Fujak
2010-12-23 13:48 ` Russell King - ARM Linux
2010-12-23 14:04 ` Tomasz Fujak
2010-12-23 14:16 ` Russell King - ARM Linux
2010-12-23 14:42 ` Felipe Contreras
2010-12-23 15:02 ` Michal Nazarewicz
2010-12-23 18:04 ` David Brown
2010-12-23 13:41 ` Michal Nazarewicz
2010-12-23 13:51 ` Russell King - ARM Linux
2010-12-23 14:08 ` Tomasz Fujak [this message]
2010-12-23 14:20 ` Russell King - ARM Linux
2010-12-23 15:35 ` Tomasz Fujak
2011-01-04 23:12 ` Jamie Lokier
2011-01-04 16:23 ` Johan MOSSBERG
2011-01-04 16:59 ` Michał Nazarewicz
2011-01-04 17:19 ` Russell King - ARM Linux
2011-01-04 17:31 ` Santosh Shilimkar
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