KVM: add halt_attempted_poll to VCPU stats

This new statistic can help diagnosing VCPUs that, for any reason,
trigger bad behavior of halt_poll_ns autotuning.

For example, say halt_poll_ns = 480000, and wakeups are spaced exactly
like 479us, 481us, 479us, 481us. Then KVM always fails polling and wastes
10+20+40+80+160+320+480 = 1110 microseconds out of every
479+481+479+481+479+481+479 = 3359 microseconds. The VCPU then
is consuming about 30% more CPU than it would use without
polling.  This would show as an abnormally high number of
attempted polling compared to the successful polls.

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com<
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index c91eb941b444..2f807ab1725e 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -63,6 +63,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
         { "exit_program_interruption", VCPU_STAT(exit_program_interruption) },
         { "exit_instr_and_program_int", VCPU_STAT(exit_instr_and_program) },
         { "halt_successful_poll", VCPU_STAT(halt_successful_poll) },
+        { "halt_attempted_poll", VCPU_STAT(halt_attempted_poll) },
         { "halt_wakeup", VCPU_STAT(halt_wakeup) },
         { "instruction_lctlg", VCPU_STAT(instruction_lctlg) },
         { "instruction_lctl", VCPU_STAT(instruction_lctl) },