Re: win7 bad i/o performance, high insn_emulation and exists

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On 20.02.2012 20:04, Gleb Natapov wrote:
On Mon, Feb 20, 2012 at 08:40:08PM +0200, Gleb Natapov wrote:
On Mon, Feb 20, 2012 at 07:17:55PM +0100, Peter Lieven wrote:
Hi,

I came a across an issue with a Windows 7 (32-bit) as well as with a
Windows 2008 R2 (64-bit) guest.

If I transfer a file from the VM via CIFS or FTP to a remote machine,
i get very poor read performance (around 13MB/s). The VM peaks at 100%
cpu and I see a lot of insn_emulations and all kinds of exists in kvm_stat

efer_reload                    0         0
exits                    2260976     79620
fpu_reload                  6197        11
halt_exits                114734      5011
halt_wakeup               111195      4876
host_state_reload        1499659     60962
hypercalls                     0         0
insn_emulation           1577325     58488
insn_emulation_fail            0         0
invlpg                         0         0
io_exits                  943949     40249
Hmm, too many of those.

irq_exits                 108679      5434
irq_injections            236545     10788
irq_window                  7606       246
largepages                   672         5
mmio_exits                460020     16082
mmu_cache_miss               119         0
mmu_flooded                    0         0
mmu_pde_zapped                 0         0
mmu_pte_updated                0         0
mmu_pte_write              13474         9
mmu_recycled                   0         0
mmu_shadow_zapped            141         0
mmu_unsync                     0         0
nmi_injections                 0         0
nmi_window                     0         0
pf_fixed                   22803        35
pf_guest                       0         0
remote_tlb_flush             239         2
request_irq                    0         0
signal_exits                   0         0
tlb_flush                  20933         0

If I run the same VM with a Ubuntu 10.04.4 guest I get around 60MB/s
throughput. The kvm_stats look a lot more sane.

efer_reload                    0         0
exits                    6132004     17931
fpu_reload                 19863         3
halt_exits                264961      3083
halt_wakeup               236468      2959
host_state_reload        1104468      3104
hypercalls                     0         0
insn_emulation           1417443      7518
insn_emulation_fail            0         0
invlpg                         0         0
io_exits                  869380      2795
irq_exits                 253501      2362
irq_injections            616967      6804
irq_window                201186      2161
largepages                  1019         0
mmio_exits                205268         0
mmu_cache_miss               192         0
mmu_flooded                    0         0
mmu_pde_zapped                 0         0
mmu_pte_updated                0         0
mmu_pte_write            7440546         0
mmu_recycled                   0         0
mmu_shadow_zapped            259         0
mmu_unsync                     0         0
nmi_injections                 0         0
nmi_window                     0         0
pf_fixed                   38529        30
pf_guest                       0         0
remote_tlb_flush             761         1
request_irq                    0         0
signal_exits                   0         0
tlb_flush                      0         0

I use virtio-net (with vhost-net) and virtio-blk. I tried disabling
hpet (which basically illiminated the mmio_exits, but does not
increase
performance) and also commit (39a7a362e16bb27e98738d63f24d1ab5811e26a8
) - no improvement.

My commandline:
/usr/bin/qemu-kvm-1.0 -netdev
type=tap,id=guest8,script=no,downscript=no,ifname=tap0,vhost=on
-device virtio-net-pci,netdev=guest8,mac=52:54:00:ff:00:d3 -drive format=host_device,file=/dev/mapper/iqn.2001-05.com.equallogic:0-8a0906-eeef4e007-a8a9f3818674f2fc-lieven-windows7-vc-r80788,if=virtio,cache=none,aio=native
-m 2048 -smp 2 -monitor tcp:0:4001,server,nowait -vnc :1 -name
lieven-win7-vc -boot order=dc,menu=off -k de -pidfile
/var/run/qemu/vm-187.pid -mem-path /hugepages -mem-prealloc -cpu
host -rtc base=localtime -vga std -usb -usbdevice tablet -no-hpet

What further information is needed to debug this further?

Which kernel version (looks like something recent)?
Which host CPU (looks like something old)?
Output of cat /proc/cpuinfo

Which Windows' virtio drivers are you using?

Take a trace like described here http://www.linux-kvm.org/page/Tracing
(with -no-hpet please).

And also "info pci" output from qemu monitor while we are at it.
here is the output while i was tracing. you can download the trace
i took while i did a ftp transfer from the vm:

-> http://82.141.21.156/report.txt.gz

QEMU 1.0 monitor - type 'help' for more information
(qemu) info pci
info pci
  Bus  0, device   0, function 0:
    Host bridge: PCI device 8086:1237
      id ""
  Bus  0, device   1, function 0:
    ISA bridge: PCI device 8086:7000
      id ""
  Bus  0, device   1, function 1:
    IDE controller: PCI device 8086:7010
      BAR4: I/O at 0xc080 [0xc08f].
      id ""
  Bus  0, device   1, function 2:
    USB controller: PCI device 8086:7020
      IRQ 5.
      BAR4: I/O at 0xc040 [0xc05f].
      id ""
  Bus  0, device   1, function 3:
    Bridge: PCI device 8086:7113
      IRQ 9.
      id ""
  Bus  0, device   2, function 0:
    VGA controller: PCI device 1234:1111
      BAR0: 32 bit prefetchable memory at 0xfd000000 [0xfdffffff].
      BAR6: 32 bit memory at 0xffffffffffffffff [0x0000fffe].
      id ""
  Bus  0, device   3, function 0:
    Ethernet controller: PCI device 1af4:1000
      IRQ 0.
      BAR0: I/O at 0xc060 [0xc07f].
      BAR1: 32 bit memory at 0xfebf0000 [0xfebf0fff].
      BAR6: 32 bit memory at 0xffffffffffffffff [0x0000fffe].
      id ""
  Bus  0, device   4, function 0:
    SCSI controller: PCI device 1af4:1001
      IRQ 0.
      BAR0: I/O at 0xc000 [0xc03f].
      BAR1: 32 bit memory at 0xfebf1000 [0xfebf1fff].
      id ""

thanks for your help,
peter

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