[Qemu-devel] Server 2012R2 guest poor performance

[Brian Rak <brak@gameservers.com>]

I'm trying to track down some CPU usage issues we're having with some 
virtual machines.  Basically, when we run our application under KVM, we 
see about 2x the CPU usage that we would see if we were running it on 
bare metal.

kvm_stat shows me the following:
  efer_reload                  0       0
  exits                120145461   54146
  fpu_reload            23548805   10735
  halt_exits            21716863    9688
  halt_wakeup           21674988    9696
  host_state_reload     30264874   14106
  hypercalls                   0       0
  insn_emulation         4459351    2087
  insn_emulation_fail          0       0
  invlpg                       0       0
  io_exits               8608533    4178
  irq_exits              4170903    1026
  irq_injections        32551242   15819
  irq_window             7779935    5332

I'm trying to figure out why I'm seeing such high numbers for VM exits, 
but I haven't been able to track down the cause yet.

If I do:

# echo 1 >/sys/kernel/debug/tracing/events/kvm/enable; cat 
/sys/kernel/debug/tracing/trace_pipe | head -100000 > trace.log ; echo 0 
 >/sys/kernel/debug/tracing/events/kvm/enable
# cat  trace.log | grep kvm_exit | awk '{print $7}' | sort | uniq -c
    4518 EXCEPTION_NMI
     427 EXTERNAL_INTERRUPT
    4048 HLT
    1870 IO_INSTRUCTION
    6819 MSR_WRITE
     188 PAUSE_INSTRUCTION
    1756 PENDING_INTERRUPT
    1775 TPR_BELOW_THRESHOLD

I've uploaded a copy of the trace log to 
https://dl.dropboxusercontent.com/u/50986796/trace.log.gz

What is causing the MSR_WRITE exits?  Is there anything I can do to 
optimize this?

I'm running:
qemu 2.2.0
'-cpu Haswell,+invtsc,hv_time,hv_relaxed,hv_vapic,hv_spinlocks=0x1000 
-no-hpet'
virtio storage + network

Is there anything else that I can do to make this run more efficiently?