RFR: 6515172: Runtime.availableProcessors() ignores Linux taskset command

[Gerald Thornbrugh]

Hi David,

I also like the idea of using an "-XX" option, that seems like the best 
way to go.

I am ok with leaving the code in.  If there are any issues with the code 
we can always
create a bug and remove it.

Jerry
> On 1/26/16 2:12 PM, David Holmes wrote:
>> Update ...
>>
>> On 22/01/2016 6:06 PM, David Holmes wrote:
>>> First a special thanks to Martin Buchholz for his input, feedback,
>>> critique and raising awareness of how non-simple this issue is.
>>>
>>> bug: https://bugs.openjdk.java.net/browse/JDK-6515172
>>> webrev: http://cr.openjdk.java.net/~dholmes/6515172/webrev/
>>>
>>> Basic problem:
>>>    processors available for use <= processors online <= processors
>>> configured
>>>
>>> but we always returned the number of online processors.
>>>
>>> Solution is simple in its basic form: use sched_getaffinity to get the
>>> scheduling affinity mask and count the number of available processors.
>>>
>>> Details are complicated by the desire to handle very large processor
>>> systems. See the bug report for lots of detailed discussions and
>>> references.
>>>
>>> Testing:
>>>   - new test that verifies behaviour when running under taskset
>>>   - diagnostic hook injection (UseNewCodeN) to enable testing of all
>>> code paths (one hook is left in for non-product to allow easy 
>>> testing of
>>> the dynamic path)
>>
>> I have been told that using the development flag UseNewCode in 
>> released code is a bad idea because it is used internally during 
>> development (as per its defined purpose).
>>
>> I would like to be able to test the dynamic path easily, but I didn't 
>> want to pay the price of adding a new VM option to do it. So choices 
>> are:
>>
>> a) don't do anything (remove the UseNewCode check)
>> b) add a new diagnostic flag
>> c) add a new experimental flag
>
> My vote:
>
> -XX:+UnlockExperimentalVMOptions -XX:+DynamicConfiguredCPUPath
>
> With a plan (and a bug) to remove that option down the road.
>
> And a code review.
>
> src/os/linux/vm/os_linux.cpp
>     No comments.
>
> src/share/vm/logging/logTag.hpp
>     No comments.
>
> test/runtime/os/AvailableProcessors.java
>     Nice test. I like that the default (no args) runs a set of tests
>     and if you (manually) run the test with a specific arg it will
>     check just that one value.
>
> Thumbs up! (Assuming you change UseNewCode to something else or
> delete its use all together.
>
> Dan
>
>
>>
>> Thoughts?
>>
>> Thanks,
>> David
>>
>>
>>>   - JPRT
>>>
>>> Compatability issues:
>>> - the system code we're using now is at least 5 years old so distro's
>>> older than that (which are not officially supported) may not work
>>> - anyone already running under a processor constrained environment 
>>> (like
>>> Docker) and using availableProcessor() to "size" things, will find that
>>> size has now changed. We do not expect this to be a problem - on the
>>> contrary we expect Docker users to want the new behaviour.
>>>
>>> Thanks,
>>> David
>