[vtk-developers] Major performance regression in VTK 6.2 to 6.3 with vtkLookupTableMapData().

[Will Schroeder]

Okay I am going to tread where I have no business going so please be
patient :-)

I'm curious as to whether anyone has tried vtkSMPTools atomics or any other
form of atomic integers....

W

On Wed, Jul 8, 2015 at 2:40 PM, Cory Quammen <cory.quammen at kitware.com>
wrote:

> Sean,
>
> I will take a look.
>
> Cory
>
> On Wed, Jul 8, 2015 at 1:11 PM, Sean McBride <sean at rogue-research.com>
> wrote:
>
>> Hi all,
>>
>> As a mentioned in another thread, we've found a big slowdown in our app
>> between 6.2 and 6.3.  Profiling with Instruments reveals lots of time is
>> being spent locking & unlocking a mutex in vtkLookupTableMapData().
>> Looking through git history shows the culprit:
>>
>> ----------------------------
>> commit dac748aedd7ffdc5aca6d555e74c668451ef4772
>> Author: Cory Quammen <cory.quammen at kitware.com>
>> Date:   Sun Mar 15 00:33:11 2015 -0400
>>
>>     BUG 15365: Fixed crash in function called from multiple threads
>>
>>     vtkLookupTableMapData() was not thread safe and could lead to
>>     crashes when accessed from multiple threads. Added a mutex around
>>     the logic to determine if the color table size needed to be
>>     increased.
>>
>>     Added a multi-threaded test that crashes on occasion prior
>>     to this patch, but does not crash with this patch applied.
>> ----------------------------
>>
>> Indeed the added code has the comment:
>>
>> // Since this involves a potential array resize and this function
>> // might be accessed concurently from more than one thread, we need a
>> // mutex here. This shouldn't affect performance much if this function
>> // is used to map many input values, but if it is called repeatedly
>> // with short input arrays, performance may be much worse.
>>
>> So, for my use case, performance is indeed much worse.  :(
>>
>> As a hack, I removed the lock/unlock and performance is back to 6.2-level.
>>
>> Help? :)
>>
>> --
>> ____________________________________________________________
>> Sean McBride, B. Eng                 sean at rogue-research.com
>> Rogue Research                        www.rogue-research.com
>> Mac Software Developer              Montréal, Québec, Canada
>>
>>
>>
>
>
> --
> Cory Quammen
> R&D Engineer
> Kitware, Inc.
>
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-- 
William J. Schroeder, PhD
Kitware, Inc.
28 Corporate Drive
Clifton Park, NY 12065
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