linux-kernel - Re: [PATCH] of: cache phandle nodes to decrease cost of of_find_node_by

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Date:   Thu, 1 Feb 2018 13:13:49 -0800
From:   Frank Rowand <frowand.list@...il.com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Chintan Pandya <cpandya@...eaurora.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of: cache phandle nodes to decrease cost of
 of_find_node_by_phandle()

On 02/01/18 06:34, Rob Herring wrote:
> On Wed, Jan 31, 2018 at 2:05 PM,  <frowand.list@...il.com> wrote:
>> From: Frank Rowand <frank.rowand@...y.com>
>>
>> Create a cache of the nodes that contain a phandle property.  Use this
>> cache to find the node for a given phandle value instead of scanning
>> the devicetree to find the node.  If the phandle value is not found
>> in the cache, of_find_node_by_phandle() will fall back to the tree
>> scan algorithm.
>>
>> The cache is initialized in of_core_init().
>>
>> The cache is freed via a late_initcall_sync().
>>
>> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
>> ---
>>
>> Some of_find_by_phandle() calls may occur before the cache is
>> initialized or after it is freed.  For example, for the qualcomm
>> qcom-apq8074-dragonboard, 11 calls occur before the initialization
>> and 80 occur after the cache is freed (out of 516 total calls.)
> 
> We should be able to do this earlier. We already walk the tree twice
> in unflattening. We can get the max phandle (or number of phandles
> IMO) on the first pass, allocate with the early allocator and then
> populate the cache in the 2nd pass. AIUI, you can alloc with memblock
> and then free with kfree as the memblock allocations get transferred
> to the slab.

Thanks for pointing out that kfree() can be used for memory alloced
with memblock.  I'll change to populate the cache earlier.