Re: [Qemu-devel] win7 bad i/o performance, high insn_emulation and exists

[Gleb Natapov]

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)?
Which Windows' virtio drivers are you using?

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

Try to use -cpu host,+x2apic. It may help Linux guest performance.

--
                        Gleb.