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

[Cory Quammen]

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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