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

[Daniil Titov]

Hi Matthias,

The change looks good to me.  Probably it also makes sense to remove method getHostConfiguredCpuCount0() since it is no longer used.

Thanks,
Daniil





On 6/12/20, 8:25 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