From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Fri, 19 Oct 2012 11:30:39 -0400
To: 9fans@9fans.net
Message-ID: <5ac1687f3033e5bc4c6a8f0896f5a974@ladd.quanstro.net>
In-Reply-To: <ed91f7ee5db4e3779d7fffb51ec5f9b7@hamnavoe.com>
References: <ed91f7ee5db4e3779d7fffb51ec5f9b7@hamnavoe.com>
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Subject: Re: [9fans] sheevaplug SD card driver
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On Fri Oct 19 10:01:11 EDT 2012, 9fans@hamnavoe.com wrote:
> > could you explain the ccmalloc trick?
>
> "cache coherent malloc" - not really a trick, just a way to
> ensure SD buffers are cache-aligned and occupy an integral
> number of cache lines, to avoid embarrassment when doing
> dma on ARM (which bypasses the cache).  It costs a bit of
> space but saves copying.

that's what i thought.

we ran into this problem and decided that it was easiest to just
cacheline-align everything in malloc, at the obvious expense of
a tiny bit of memory.  the reason for this was we were using a few
kw devices that could get just about any chunk of malloc'd memory.

ideally we would have written a kw-specific malloc with tracking
segregated from the managed memory.

- erik