[alsa-devel] [PATCH 1/2 v2] ASoC: soc-cache: block based rbtree compression
dp at opensource.wolfsonmicro.com
Mon May 2 16:40:20 CEST 2011
On Mon, May 02, 2011 at 04:29:01PM +0200, Takashi Iwai wrote:
> At Mon, 2 May 2011 13:28:28 +0100,
> Dimitris Papastamos wrote:
> > This patch prepares the ground for the actual rbtree optimization patch
> > which will save a pointer to the last accessed register block that was used
> > in either the read() or write() functions.
> > Each node manages a block of up to RBTREE_BLOCK_NUM registers. There can be
> > no two nodes with overlapping blocks. Currently there is no check in the code
> > to scream in case that ever happens. Each block has a base and top register,
> > all others lie in between these registers. Note that variable length blocks
> > aren't supported. So if you have an interval [8, 15] and only some of those
> > registers actually exist on the device, the block will have the non-existent
> > registers as zero. There is also no way of reporting that any of those
> > non-existent registers were accessed/modified.
> > The larger the block size, the more probable it is that one of the
> > managed registers is non-zero, and therefore the node will need to be
> > allocated at initialization time and waste space.
> > If register N is accessed and it is not part of any of the current
> > blocks in the rbtree, a new node is created with a base register
> > which is floor(N / RBTREE_BLOCK_NUM) * RBTREE_BLOCK_NUM and a top
> > register as base_register + RBTREE_BLOCK_NUM - 1. All other registers
> > in the block are initialized as expected and the node is inserted into
> > the tree.
> > Signed-off-by: Dimitris Papastamos <dp at opensource.wolfsonmicro.com>
> Looking through the patch, I wonder whether it gives a performance
> gain enough for the additional complexity. Did you measure somehow?
This patch itself does not provide a performance benefit. The next
patch in line which caches the last used block will provide a
performance benefit. I have planted some cache hit/miss counters in my
debug code to measure this. Ideally it'd be nice for the codec
drivers/machine drivers to be able to tune the block size at init time.
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