Hi, I ran following command, ./x86_64-softmmu/qemu-system-x86_64 -k en-us --show-cursor --enable-kvm -smp 2 -m 1024 -hda /var/opt/kvm/img/ubuntu14.04.img -drive if=none,id=drive1,cache=none,format=raw,aio=native,file=cvbd:// 127.0.0.1:6380/win7.img?block_size=4096 -device virtio-blk,drive=drive1 -vnc :0 perf out shoed me 14.31% send_full_color_rect.isra.12. Following is the output of 14.31% qemu-system-x86 libz.so.1.2.8 [.] 0x0000000000002ae7 ◆ - 0x7f6660d67ae7 ▒ + 0x7f6660d68968 ▒ + deflate ▒ - tight_compress_data ▒ - 14.31% send_full_color_rect.isra.12 ▒ send_sub_rect ▒ - tight_send_framebuffer_update ▒ 14.23% vnc_worker_thread_loop ▒ - 0.08% tight_send_framebuffer_update ▒ - 0.05% tight_send_framebuffer_update ▒ - tight_send_framebuffer_update ▒ 0.03% vnc_worker_thread_loop ▒ - 0.01% tight_send_framebuffer_update ▒ vnc_worker_thread_loop ▒ 0.03% vnc_worker_thread_loop ▒ - 0.00% send_sub_rect ▒ tight_send_framebuffer_update ▒ vnc_worker_thread_loop ▒ + 4.68% qemu-system-x86 libz.so.1.2.8 [.] 0x0000000000002ac0 ▒ + 3.65% qemu-system-x86 libz.so.1.2.8 [.] 0x0000000000002ae1 ▒ + 3.56% qemu-system-x86 libz.so.1.2.8 [.] 0x0000000000002ad0 ▒ + 2.71% qemu-system-x86 libz.so.1.2.8 [.] 0x0000000000002ac7 ▒ + 2.31% qemu-system-x86 qemu-system-x86_64 [.] vnc_refresh_server_surface ▒ - 1.90% qemu-system-x86 [kernel.kallsyms] [k] vcpu_enter_guest Following are the commands that I ran, root@Machine3:~# perf record --call-graph dwarf -p 4101 ^C[ perf record: Woken up 2141 times to write data ] [ perf record: Captured and wrote 536.328 MB perf.data (~23432515 samples) ] root@Machine3:~# perf report -g graph --no-children root@Machine3:~# uname -a Linux Machine3 3.16.0-46-generic #62~14.04.1-Ubuntu SMP Tue Aug 11 16:27:16 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux root@Machine3:~# egrep -c '(vmx|svm)' /proc/cpuinfo 4 root@Machine3:~# kvm-ok INFO: /dev/kvm exists KVM acceleration can be used Any reason why its taking so much time. Thanks, Darshan