RFR: 8146115 - Improve docker container detection and resource configuration usage

[Bob Vandette]

Robbin,

I’ve looked into this issue and you are correct.  I do have to examine both the
sched_getaffinity results as well as the cgroup cpu subsystem configuration
files in order to provide a reasonable value for active_processors.  If I was only
interested in cpusets, I could simply rely on the getaffinity call but I also want to
factor in shares and quotas as well.

I had assumed that when sched_setaffinity was called (in your case by numactl) that the 
cgroup cpu config files would be updated to reflect the current processor affinity for the 
running process. This is not correct.  I have updated my changeset and have successfully
run with your examples below.  I’ll post a new webrev soon.

Thanks,
Bob.


> 
>> I still want to include the flag for at least one Java release in the event that the new behavior causes some regression
>> in behavior.  I’m trying to make the detection robust so that it will fallback to the current behavior in the event
>> that cgroups is not configured as expected but I’d like to have a way of forcing the issue.  JDK 10 is not
>> supposed to be a long term support release which makes it a good target for this new behavior.
>> I agree with David that once we commit to cgroups, we should extract all VM configuration data from that
>> source.  There’s more information available for cpusets than just processor affinity that we might want to
>> consider when calculating the number of processors to assume for the VM.  There’s exclusivity and
>> effective cpu data available in addition to the cpuset string.
> 
> cgroup only contains limits, not the real hard limits.
> You most consider the affinity mask. We that have numa nodes do:
> 
> [rehn at rehn-ws dev]$ numactl --cpunodebind=1 --membind=1 java -Xlog:os=debug -cp . ForEver | grep proc
> [0.001s][debug][os] Initial active processor count set to 16
> [rehn at rehn-ws dev]$ numactl --cpunodebind=1 --membind=1 java -Xlog:os=debug -XX:+UseContainerSupport -cp . ForEver | grep proc
> [0.001s][debug][os] Initial active processor count set to 32
> 
> when benchmarking all the time and that must be set to 16 otherwise the flag is really bad for us.
> So the flag actually breaks the little numa support we have now.
> 
> Thanks, Robbin