From: Eugene Surovegin <ebs@ebshome•net>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: debian-powerpc@lists•debian.org, linuxppc-dev@ozlabs•org
Subject: Re: Not coherent cache DMA for G3/G4 CPUs: clarification needed
Date: Thu, 20 Apr 2006 14:33:16 -0700 [thread overview]
Message-ID: <20060420213316.GD25755@gate.ebshome.net> (raw)
In-Reply-To: <1145567174.4517.1.camel@localhost.localdomain>
On Fri, Apr 21, 2006 at 07:06:13AM +1000, Benjamin Herrenschmidt wrote:
> (On 6xx this is deadly even if you don't access those cacheable pages
> because the CPU prefetch may do it for you).
Here is another thought if this "prefetch" theory is correct.
You guys seems to focus on
dma_alloc_coherent()/pci_alloc_consistent(), but forgeting about so
called "streaming" mappings.
You cannot just flush/invalidate cache any more, because "CPU can
prefetch this data back". So, to be completely correct (if you insist
on "6xx can prefetch"-theory), you have to actually _copy_ data to
your consistent memory on dma_map_single(). You can imagine
performance implications. I suspect even 440 will be faster in this
case than G4 :).
--
Eugene
next prev parent reply other threads:[~2006-04-20 21:33 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-20 18:57 Not coherent cache DMA for G3/G4 CPUs: clarification needed Gerhard Pircher
2006-04-20 20:38 ` Eugene Surovegin
2006-04-20 20:56 ` Gerhard Pircher
2006-04-20 21:02 ` Eugene Surovegin
2006-04-20 21:10 ` Gerhard Pircher
2006-04-20 21:55 ` Eugene Surovegin
2006-04-20 22:08 ` Gerhard Pircher
2006-04-24 19:21 ` Mark A. Greer
2006-04-21 4:38 ` Benjamin Herrenschmidt
2006-04-21 8:03 ` Gerhard Pircher
2006-04-21 14:33 ` Brent Cook
2006-04-21 21:51 ` Benjamin Herrenschmidt
2006-04-27 21:31 ` Mark A. Greer
2006-04-27 21:53 ` Benjamin Herrenschmidt
2006-04-27 22:08 ` Mark A. Greer
2006-04-29 17:57 ` Gerhard Pircher
2006-04-20 21:06 ` Benjamin Herrenschmidt
2006-04-20 21:13 ` Eugene Surovegin
2006-04-20 21:19 ` Eugene Surovegin
2006-04-20 22:40 ` Benjamin Herrenschmidt
2006-04-20 22:39 ` Benjamin Herrenschmidt
2006-04-20 23:46 ` Gabriel Paubert
2006-04-21 0:09 ` Benjamin Herrenschmidt
2006-04-20 21:33 ` Eugene Surovegin [this message]
2006-04-20 22:41 ` Benjamin Herrenschmidt
2006-04-21 8:21 ` Gerhard Pircher
2006-04-20 21:03 ` Benjamin Herrenschmidt
2006-04-20 21:33 ` Gerhard Pircher
2006-04-20 22:07 ` Gabriel Paubert
2006-04-20 22:26 ` Gerhard Pircher
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