[alsa-devel] [PATCH 2/2] ASoC: dapm: Add cache to speed up adding of routes

[Lars-Peter Clausen]

On 05/07/2015 12:33 PM, Charles Keepax wrote:
> Some CODECs have a significant number of DAPM routes and for each route,
> when it is added to the card, the entire card widget list must be
> searched. When adding routes it is very likely, however, that adjacent
> routes will require adjacent widgets. For example all the routes for a
> mux are likely added in a block and the sink widget will be the same
> each time and it is also quite likely that the source widgets are
> sequential located in the widget list.
>
> This patch adds an optional cache argument to snd_soc_dapm_add_route, if
> given, this argument will hold the source and sink widgets from the last
> call to snd_soc_dapm_add_route. A small search of the widget list will
> be made from those points for both the sink and source. Currently this
> search only checks both the last widget and the one adjacent to it.
>
> On wm8280 which has approximately 500 widgets and 30000 routes (one of
> the largest CODECs in mainline), the number of paths that hit the cache
> is 24000, which significantly improves probe time.

That's crazy! ;)

I wonder if it makes sense to come up with a more machine readable blob 
format that can be pre-compiled where we don't have to search the widget 
list each time a route is added. Instead of having it reference the widgets 
by name use a index that points into an array of widgets. That makes the 
lookup time O(1).

>
> Signed-off-by: Charles Keepax <ckeepax at opensource.wolfsonmicro.com>
> ---
>   sound/soc/soc-dapm.c |   40 ++++++++++++++++++++++++++++++++++++++--
>   1 files changed, 38 insertions(+), 2 deletions(-)
>
> diff --git a/sound/soc/soc-dapm.c b/sound/soc/soc-dapm.c
> index ea3348e..95d3ea5 100644
> --- a/sound/soc/soc-dapm.c
> +++ b/sound/soc/soc-dapm.c
> @@ -2585,8 +2585,26 @@ err:
>   	return ret;
>   }
>
> +static struct snd_soc_dapm_widget *
> +dapm_check_path_cache(const char *name, struct snd_soc_dapm_widget *w, int n)
> +{
> +	int i;
> +
> +	if (w) {
> +		for (i = 0; i < n; i++) {
> +			if (!strcmp(name, w->name))
> +				return w;
> +
> +			w = list_next_entry(w, list);

This will return garbage if w is the last widget in the list.

Otherwise the patch looks sensible.