RFR: 8247469: getSystemCpuLoad() returns -1 on linux when some offline cpus are present and cpusets.effective_cpus is not available

[Bob Vandette]

Look good to me.

Bob.


> On Jun 12, 2020, at 11:01 AM, Baesken, Matthias <matthias.baesken at sap.com> wrote:
> 
> Hello, please review  the  following  change .
> We have a Linux machine  where 
>           OperatingSystemMXBean mbean = (com.sun.management.OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
>             double load = mbean.getSystemCpuLoad();
> returns -1  ; 
> 
> Reason is that  there are offline CPUs  (48 configured ,  32 online ). Additionally   cpusets.effective_cpus  is not available on that Linux system .
> 
> 
> Bug/webrev :
> 
> https://bugs.openjdk.java.net/browse/JDK-8247466
> 
> http://cr.openjdk.java.net/~mbaesken/webrevs/8247469.0/
> 
> 
> Thanks, 
>        Matthias
> 
> 
> -----Original Message-----
> From: Bob Vandette <bob.vandette at oracle.com> 
> Sent: Freitag, 12. Juni 2020 15:02
> To: Baesken, Matthias <matthias.baesken at sap.com>
> Cc: daniil.x.titov at oracle.com
> Subject: Re: getCpuLoad() / getSystemCpuLoad() returns -1 on linux when some offline cpus are present and cpusets.effective_cpus is not available
> 
> I looks like there are two problems here:
> 
> 1. containerMetrics.getCpuSetCpus().length returns the online CPUs but getHostConfiguredCpuCount0() returns the total number of CPUs including offline ones.
> 
> One solution might be to add a getHostOnlineCpuCount0() function.
> 
> 2. If getEffectiveCpuSetCpus is not available then we should use getCpuSetCpus.
> 
> Bob.
> 
> 
>> On Jun 12, 2020, at 6:43 AM, Baesken, Matthias <matthias.baesken at sap.com> wrote:
>> 
>> Hello, I noticed the following on  one of our Linux machines :
>> 
>>            OperatingSystemMXBean mbean = (com.sun.management.OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
>>            double load = mbean.getSystemCpuLoad();
>> 
>> returns -1  ; this seems to be related to   “8226575: OperatingSystemMXBean should be made container aware”   .
>> 
>> This machine has the following “special  features” 
>> 
>> - a few CPUs are offline (means the configured cpus are 48 but the online cpus are 32) so 
>> 
>> 
>>    private boolean isCpuSetSameAsHostCpuSet() {
>>        if (containerMetrics != null && containerMetrics.getCpuSetCpus() != null) {
>>            return containerMetrics.getCpuSetCpus().length == getHostConfiguredCpuCount0();
>>        }
>>        return false;
>>    }
>> 
>> Returns false
>> 
>> - the machine does not have cpusets.effective_cpus    (not all Linux machines have it )
>> 
>> In this case getSystemCpuLoad() / getCpuLoad() returns -1 (because it checks that 48 != 32, and next it checks for cpusets.effective_cpus which is not present ).
>> 
>> See the coding at :
>> https://hg.openjdk.java.net/jdk/jdk/file/bdc14b8d31ff/src/jdk.management/unix/classes/com/sun/management/internal/OperatingSystemImpl.java#l136
>> 
>>                // If the cpuset is the same as the host's one there is no need to iterate over each CPU
>>                if (isCpuSetSameAsHostCpuSet()) {
>>                    return getCpuLoad0();
>>                } else {
>>                    int[] cpuSet = containerMetrics.getEffectiveCpuSetCpus();
>>                    if (cpuSet != null && cpuSet.length > 0) {
>>                        double systemLoad = 0.0;
>>                        for (int cpu : cpuSet) {
>>                            double cpuLoad = getSingleCpuLoad0(cpu);
>>                            if (cpuLoad < 0) {
>>                                return -1;
>>                            }
>>                            systemLoad += cpuLoad;
>>                        }
>>                        return systemLoad / cpuSet.length;
>>                    }
>>                    return -1;
>>                }
>> 
>> 
>> Could  we better a)  return  the native getCpuLoad0();  in this case   or  b)  use the  available  containerMetrics.getCpuSetCpus(); when getEffectiveCpuSetCpus();
>> Gives an empty array   (btw.   getCpuSetCpus()   returns  on this machine the online cpus = 0,31 = 32 ) ?
>> 
>> I opened
>> 
>> https://bugs.openjdk.java.net/browse/JDK-8247469
>> 
>> to track this   (I see the issue  in jdk/jdk   but   it seems  it came also  to  oracle jdk8u261,  which the July update ).
>> 
>> Best regards, Matthias
>