Further Windows performance optimizations?

Further Windows performance optimizations?

[Brian Rak]

Are there any optimizations that I can do for EOI/APIC for a Windows 
2008R2 guest?  I'm seeing a significant amount of kernel CPU usage from 
kvm_ioapic_update_eoi.  I can't seem to find any information on further 
optimizations for this.

Sample of trace output: 
https://gist.github.com/devicenull/d1a918879d38955053dd/raw/3aed63b8e60e98c3e7fe21a42ca123d8bf309e0c/trace

Host setup:
3.10.9-1.el6.x86_64 #1 SMP Tue Aug 27 15:27:08 EDT 2013 x86_64 x86_64 
x86_64 GNU/Linux with this patchset applied: 
http://www.spinics.net/lists/kvm/msg91214.html
CentOS 6
qemu 1.6.0 (also patched with the above enlightenment)
2x Intel E5-2630 (virtualization extensions turned on, total of 24 cores 
including hyperthread cores)
24GB memory
swap file is enabled, but unused

Guest setup:
Windows Server 2008R2 (64 bit)
24 vCPUs
20 GB memory
VirtIO disk drivers
SR-IOV for network (with Intel I350 network chipset)
/usr/libexec/qemu-kvm -name VMID109 -S -machine 
pc-i440fx-1.6,accel=kvm,usb=off -cpu 
host,hv_relaxed,hv_vapic,hv_spinlocks=0x1000 -m 20480 -smp 
24,sockets=1,cores=12,threads=2 -uuid 
6a7517f5-3b1c-43c2-aa71-96b143356b3d -no-user-config -nodefaults 
-chardev 
socket,id=charmonitor,path=//var/lib/libvirt/qemu/VMID109.monitor,server,nowait 
-mon chardev=charmonitor,id=monitor,mode=readline -rtc 
base=utc,driftfix=slew -no-hpet -boot c -usb -drive 
file=/dev/vmimages/VMID109,if=none,id=drive-virtio-disk0,format=raw,cache=none,aio=native 
-device 
virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 
-drive if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw 
-device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -vnc 
127.0.0.1:109 -k en-us -vga cirrus -device 
pci-assign,host=02:10.0,id=hostdev0,bus=pci.0,addr=0x3,rombar=1,romfile=/usr/share/gpxe/80861520.rom 
-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5


I removed a bunch of empty entries from below:
# perf stat -e 'kvm:*' -a sleep 1m

  Performance counter stats for 'sleep 1m':

          9,707,680 kvm:kvm_entry [100.00%]
              8,199 kvm:kvm_hv_hypercall [100.00%]
            188,418 kvm:kvm_pio [100.00%]
                  6 kvm:kvm_cpuid [100.00%]
          3,983,787 kvm:kvm_apic [100.00%]
          9,715,744 kvm:kvm_exit [100.00%]
          4,028,354 kvm:kvm_inj_virq [100.00%]
          3,245,823 kvm:kvm_msr [100.00%]
             185,573 kvm:kvm_pic_set_irq [100.00%]
            741,665 kvm:kvm_apic_ipi [100.00%]
          2,518,242 kvm:kvm_apic_accept_irq [100.00%]
          2,506,003 kvm:kvm_eoi [100.00%]
            125,532 kvm:kvm_emulate_insn [100.00%]
            187,912 kvm:kvm_userspace_exit [100.00%]
            309,091 kvm:kvm_set_irq [100.00%]
            186,014 kvm:kvm_ioapic_set_irq [100.00%]
            124,458 kvm:kvm_msi_set_irq [100.00%]
          1,475,484 kvm:kvm_ack_irq [100.00%]
          1,295,360 kvm:kvm_fpu [100.00%]

       60.001063613 seconds time elapsed

perf top -G output:

-  25.65%  [kernel]                    [k] _raw_spin_lock
    - _raw_spin_lock
       - 98.63% kvm_ioapic_update_eoi
kvm_ioapic_send_eoi
apic_set_eoi
apic_reg_write
kvm_hv_vapic_msr_write
set_msr_hyperv
kvm_set_msr_common
vmx_set_msr
handle_wrmsr
vmx_handle_exit
vcpu_enter_guest
__vcpu_run
kvm_arch_vcpu_ioctl_run
kvm_vcpu_ioctl
do_vfs_ioctl
SyS_ioctl
system_call_fastpath
          + __GI___ioctl