Integrated: 8273972: Multi-core choke point in CMM engine (LCMSTransform.doTransform)

[Sergey Bylokhov]

On Fri, 24 Sep 2021 04:38:13 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

> Initially, the bug was discussed here:
> https://stackoverflow.com/questions/35264582/why-is-multithreading-slowing-down/35264813
> 
> The root cause is that if for some reason directly or indirectly the color transform object is shared across the threads it cannot be used for parallel color transformation because the method LCMSTransform.doTransform()  is synchronized.
> 
> This code seems to be created when the littlecms 1.x was used which was not thread-safe, but the latest version is thread safe (subject to bugs). I can check that by compiling lcms with #define CMS_NO_PTHREADS which will cause some of our tests fail here and there.
> 
> To check that transform can be used across the threads I created two quite heavyweight tests which tests different color transformations using different threads.
> 
> The fix moves the data for the native transform from the LCMSTransform object to the NativeTransform class just to simplify synchronization steps, so only one volatile read of "transform" is executed in the common path.
> 
> Result for the testcase attached to SO: https://stackoverflow.com/a/35264713
> |№ threads|Before the fix|After the fix|
> |-------------|-------------|-------------|
> |1 |  693 ms | 699 ms|
> |8 | 6641 ms| 873 ms|
> |30 |34069 ms|1034 ms|

This pull request has now been integrated.

Changeset: e49e5b5a
Author:    Sergey Bylokhov <serb at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/e49e5b5a7ed9e493380fb73100057898c707b31b
Stats:     358 lines in 5 files changed: 317 ins; 25 del; 16 mod

8273972: Multi-core choke point in CMM engine (LCMSTransform.doTransform)

Reviewed-by: prr

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PR: https://git.openjdk.java.net/jdk/pull/5671