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 00:59:02 -0800
From:   Frank Rowand <frowand.list@...il.com>
To:     Chintan Pandya <cpandya@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...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 01/31/18 22:45, Chintan Pandya wrote:
> 
> 
> On 2/1/2018 1:35 AM, frowand.list@...il.com wrote:
>> From: Frank Rowand <frank.rowand@...y.com>
> 
>> +
>> +static void of_populate_phandle_cache(void)
>> +{
>> +    unsigned long flags;
>> +    phandle max_phandle;
>> +    u32 nodes = 0;
>> +    struct device_node *np;
>> +
>> +    if (phandle_cache)
>> +        return;
>> +
>> +    max_phandle = live_tree_max_phandle();
>> +
>> +    raw_spin_lock_irqsave(&devtree_lock, flags);
>> +
>> +    for_each_of_allnodes(np)
>> +        nodes++;
>> +
>> +    /* sanity cap for malformed tree */
>> +    if (max_phandle > nodes)
>> +        max_phandle = nodes;
> Shouldn't we speak up about this in kernel log ? May be WARN_ON() ?

Probably not.  If we care enough about a hand coded phandle property
value we should add a check to checkpatch and/or dtc instead of adding
the warning here.


>> +
>> +    phandle_cache = kzalloc((max_phandle + 1) * sizeof(*phandle_cache),
>> +                GFP_KERNEL);
> kzalloc (might_sleep) in critical context will break.

Yes, thanks.

I also need to ensure memory ordering in of_free_phandle_cache()
to ensure that max_phandle_cache is zero before the cache memory
is freed.


> Anyways, will fix this locally and share test results.

Thanks, I look forward to the results.


> Thanks,
> Chintan
>