Re: [PATCH] of: use hash based search in of_find_node_by_phandle

On Fri, Jan 26, 2018 at 1:22 AM, Chintan Pandya [off-list ref] wrote:

On 1/25/2018 8:20 PM, Rob Herring wrote:

quoted

On Thu, Jan 25, 2018 at 4:14 AM, Chintan Pandya [off-list ref]
wrote:

quoted

[...]

quoted

I'd guess that there's really only a few phandle lookups that occur
over and over.

On my system, there are ~6.7k calls of this API during boot.

And after boot it will be near 0 yet we carry the memory usage forever.

quoted

The clock controller, interrupt controller, etc. What
if you just had a simple array of previously found nodes for a cache
and of_find_node_by_phandle can check that array first. Probably 8-16
entries would be enough.

I clearly see repeat calling with same phandle. But I have few hundreds of
nodes.
I see hashing as generic optimization which applies equally good to all
sized DT.
Using ~4KB more size to save 400 ms is a good trade-off, I believe.

But if you can use 200 bytes and save 350 ms, that would be a better
trade off IMO. But we don't know because we have no data.

Rob