RFR: 8227006 - [linux] Runtime.availableProcessors execution time increased by factor of 100

[Claes Redestad]

One timeout value per subsystem seems reasonable for now, and the logic
seems clearer now. Looks good!

/Claes

On 2019-10-30 19:35, Bob Vandette wrote:
> Summary:  The container support added to Linux caused the call to os::active_processor_count to
> become much more expensive than prior to the container addition.  This RFR adds a cache to avoid
> the extra overhead on repetitive calls to Runtime.getRuntime().availableProcessors().  The cache
> timeout is set at 20ms.  This allows the docker update command to alter the number of available processors
> which will be reflected in the return from the API.
> 
> BUG: https://bugs.openjdk.java.net/browse/JDK-8227006
> WEBREV:  http://cr.openjdk.java.net/~bobv/8227006/webrev.01
> 
> Adding a single cache of active_processor_count with a 20ms timeout results in the following improvements.
> 
> ORIGINAL SCORES
> 
> 39346 calls/sec
> 40007 calls/sec
> 39708 calls/sec
> 39732 calls/sec
> 39736 calls/sec
> 39629 calls/sec
> 
> DISABLE CONTAINER SUPPORT (-XX:-UseContainerSupport)
> 
> 1106795 calls/sec
> 1135589 calls/sec
> 1123782 calls/sec
> 1123605 calls/sec
> 1123343 calls/sec
> 1123135 calls/sec
> 
> 20MS TIMEOUT CACHE
> 
> 9867172 calls/sec
> 10077977 calls/sec
> 9989674 calls/sec
> 9983963 calls/sec
> 9984400 calls/sec
> 9985898 calls/sec
> 9985123 calls/sec
> 9985608 calls/sec
> 
> So the cache actually improves performance beyond the pre-container support by 8x but
> this of course only helps programs that call this function in a loop.
> 
> 
> Bob.
> 
> 
>