RFR: 8058935: CPU detection gives 0 cores per cpu, 2 threads per core in Amazon EC2 environment

[Vladimir Kozlov]

According to next document the cpu has 10 cores (and 2 threads per core):

http://ark.intel.com/products/75275/Intel-Xeon-Processor-E5-2670-v2-25M-Cache-2_50-GHz

hs_err in the bug report reports only 2 processors and next lines are 
missing:

physical id	: 0
siblings	: 4
core id		: 0
cpu cores	: 4
apicid		: 0
initial apicid	: 0

I assume it is some kind of virtual environment with which cpuid 
topology is not working (at least our code does not work).
We may missing some checks which indicates that topology is not supported.
It would be nice if you can put all topology and related cpuid bits from 
amazon ec2 in bug report.
Checking for 0 could be fine but if it is not 0 it could be still wrong 
if topology info is not supported.

Thanks,
Vladimir

On 11/17/14 8:20 AM, Vladimir Kempik wrote:
> Hi,
>
> Please review patch adding sanity check to cores_per_cpu():
>
> http://cr.openjdk.java.net/~vkempik/8058935/webrev.00/
> https://bugs.openjdk.java.net/browse/JDK-8058935
>
> Few months ago we've got reports of java crashing in amazon ec2
> enviroment (they use Xen).
> https://bugs.openjdk.java.net/browse/JDK-8058935
> https://bugs.openjdk.java.net/browse/JDK-8058937
>
> JVM args was used to make the crash: -XX:+UnlockCommercialFeatures
> -XX:+FlightRecorder
>
> After investigation I think the crash could only have happened if
> support_processor_topology() returned true and
> _cpuid_info.tpl_cpuidB1_ebx.bits.logical_cpus was zero.
>
> I wasn't able to reproduce the bug on amazon ec2 cloud in present days.
>
> The patch adds sanity check, if cpu topology was used and resulted in 0
> cores per cpu, then fallback to non-topology variant, which can't result
> in 0 cores per cpu.
>
> Testing: JPRT.
>
> Thanks,
> Vladimir.