• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Accumulate timing information for real-mode code · b6c295df
    Paul Mackerras authored
    This reads the timebase at various points in the real-mode guest
    entry/exit code and uses that to accumulate total, minimum and
    maximum time spent in those parts of the code.  Currently these
    times are accumulated per vcpu in 5 parts of the code:
    
    * rm_entry - time taken from the start of kvmppc_hv_entry() until
      just before entering the guest.
    * rm_intr - time from when we take a hypervisor interrupt in the
      guest until we either re-enter the guest or decide to exit to the
      host.  This includes time spent handling hcalls in real mode.
    * rm_exit - time from when we decide to exit the guest until the
      return from kvmppc_hv_entry().
    * guest - time spend in the guest
    * cede - time spent napping in real mode due to an H_CEDE hcall
      while other threads in the same vcore are active.
    
    These times are exposed in debugfs in a directory per vcpu that
    contains a file called "timings".  This file contains one line for
    each of the 5 timings above, with the name followed by a colon and
    4 numbers, which are the count (number of times the code has been
    executed), the total time, the minimum time, and the maximum time,
    all in nanoseconds.
    
    The overhead of the extra code amounts to about 30ns for an hcall that
    is handled in real mode (e.g. H_SET_DABR), which is about 25%.  Since
    production environments may not wish to incur this overhead, the new
    code is conditional on a new config symbol,
    CONFIG_KVM_BOOK3S_HV_EXIT_TIMING.
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
    b6c295df
Kconfig 5.65 KB