From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Michal Nazarewicz <mina86@mina86.com>
Cc: 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 13:51:20 +0000 [thread overview]
Message-ID: <20101223135120.GL3636@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <87k4j0ehdl.fsf@erwin.mina86.com>
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.
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next prev parent reply other threads:[~2010-12-23 13:52 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-15 20:34 [PATCHv8 00/12] Contiguous Memory Allocator 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 [this message]
2010-12-23 14:08 ` Tomasz Fujak
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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