Performance drop when updating > 500k pixels

[Pierre Ossman]

On 12/01/17 13:53, Pierre Ossman wrote:
> 
> For small updates I see performance growing logarithmically, measured in
> pixels/second. At around 500k pixels it starts leveling off at ~1.5
> Gpixels/second. After that the performance starts dropping linearly as
> the update grows.

I'll answer myself here...

This seems to be a CPU cache issue. Below this limit I see:

         4,469,985      cache-misses:u            #    0.336 % of all cache refs    
    35,279,259,258      instructions:u            #    1.70  insn per cycle                                              (100.00%)

Above the limit I get:

       194,571,782      cache-misses:u            #   30.322 % of all cache refs    
    18,084,891,734      instructions:u            #    0.73  insn per cycle                                            

So no wonder things take a turn for the worse.

I'll have to think a bit on how to make this more efficient. Ideas are always welcome.

Regards
-- 
Pierre Ossman           Software Development
Cendio AB               https://cendio.com
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Phone: +46-13-214600    https://plus.google.com/+CendioThinLinc

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