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

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Date:   Fri, 2 Feb 2018 13:26:25 -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 02/01/18 21:59, Chintan Pandya wrote:
> 
> 
> On 2/2/2018 12:40 AM, Frank Rowand wrote:
>> On 02/01/18 02:31, Chintan Pandya wrote:
>>>
>>>>> Anyways, will fix this locally and share test results.
>>>>
>>>> Thanks, I look forward to the results.
>>>>
>>>
>>> Set up for this time was slightly different. So, taken all the numbers again.
>>>
>>> Boot to shell time (in ms): Experiment 2
>>> [1] Base            : 14.843805 14.784842 14.842338
>>> [2] 64 sized fixed cache    : 14.189292 14.200003 14.266711
>>> [3] Dynamic freeable cache    : 14.112412 14.064772 14.036052
>>>
>>> So, [3] (this patch) looks to be improving 750ms (on avg from base build).
>>>
>>
>> Is this with the many debug options enabled?  If so, can you repeat with
>> a normal configuration?
> 
> Could you share me the point of doing this experiment in perf mode ?

You had mentioned earlier in another thread:

   My recent results were taken on debug_defconfig which has many performance
   slowing code. So, gap between base-build and w/ the test patches would be
   more than the actual production build.

If you measure a large performance gain with a debug configuration, that
may not represent the actual gain you will get with a production
configuration, as you noted.

My question was trying to determine whether the numbers reported above
are for a debug configuration or a production configuration.  And if
not a production configuration, I was requesting the numbers for a
production configuration.  If the production configuration does not
show a significant boot time reduction from the patch then there is
less justification for adding complexity to the existing code.  I
prefer to use simpler data structures and algorithms __if__ extra
complexity does not provide any advantage.  The balance between
complexity and benefits is a core software engineering issue.

> I don't have a set up for taking these numbers in perf mode. For
> that, I need to ask some other team and round trip follow ups. In my
> set up, I rely on serial console logging which gets disabled in perf
> mode.
> 
>>
>> Thanks,
>>
>> Frank
>>
> 
> Chintan