Re: [PATCH] of: use hash based search in of_find_node_by_phandle
From: Chintan Pandya
Date: Fri Jan 26 2018 - 02:23:20 EST
On 1/25/2018 8:20 PM, Rob Herring wrote:
On Thu, Jan 25, 2018 at 4:14 AM, Chintan Pandya <cpandya@xxxxxxxxxxxxxx> wrote:
of_find_node_by_phandle() takes a lot of time finding
Got some numbers for what is "a lot of time"?
On my SDM device, I see total saving of 400ms during boot time. For some
clients
whose node is quite deeper, they see 1ms time taken by this API.
right node when your intended device is too right-side
in the fdt. Reason is, we search each device serially
from the fdt, starting from left-most to right-most.
By right side, you mean a deep path?
Yes, will correct this if original is confusing.
Implement, device-phandle relation in hash-table so
that look up can be faster.
Change-Id: I4a2bc7eff6de142e4f91a7bf474893a45e61c128
Run checkpatch.pl
Sure. My bad.
@@ -61,6 +62,7 @@ struct device_node {
struct kobject kobj;
unsigned long _flags;
void *data;
+ struct hlist_node hash;
Always base your patches on the latest -rc at least. This won't apply.
Ok, sure.
This grows struct device_node for every single node which we recently
worked on to shrink (which is why this won't apply). So I'm now
sensitive to anything that grows it. I'd really prefer something out
of band.
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.
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.
Chintan Pandya
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