Friday, July 29, 2016

Linux kernel 4.7 released

In Linux kernel 4.7 (available here), we improved usability of the kvm_stat tool for z Systems, introducing (among others) new option -p to filter by process ID.

Using kvm_stat, one can monitor e.g. the number of SIE exits or specific diags to investigate performance issues:
  kvm statistics - summary

   Event                                        Total Current
   kvm_s390_sie_enter                          621113      96
   kvm_s390_sie_exit                           621113      96
   kvm_vcpu_wakeup                             231054      69
   kvm_s390_intercept_instruction              187720      24
   kvm_halt_poll_ns                            131133      15
   kvm_s390_handle_diag                         64543      12
   kvm_userspace_exit                            1427      11
   kvm_s390_handle_sigp                        121746       1
   kvm_set_irq                                 154402       0
   kvm_s390_handle_sigp_pei                     18407       0
   kvm_s390_handle_stsi                            12       0
   kvm_s390_handle_stfl                             1       0
Use option -p to further investigate specific QEMU processes to identify the potential culprits:
  $ ./kvm_stat -p 4304 -1 | grep kvm_s390_sie
  kvm_s390_sie_enter                              3985      3985
  kvm_s390_sie_exit                               3985      3985
  kvm_s390_sie_fault                                 0         0

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