I wanted to share some performance data for KVM and Xen. I thought it would be interesting to share some performance results especially compared to Xen, using a more complex situation like heterogeneous server consolidation.
The Workload: The workload is one that simulates a consolidation of servers on to a single host. There are 3 server types: web, imap, and app (j2ee). In addition, there are other "helper" servers which are also consolidated: a db server, which helps out with the app server, and an nfs server, which helps out with the web server (a portion of the docroot is nfs mounted). There is also one other server that is simply idle. All 6 servers make up one set. The first 3 server types are sent requests, which in turn may send requests to the db and nfs helper servers. The request rate is throttled to produce a fixed amount of work. In order to increase utilization on the host, more sets of these servers are used. The clients which send requests also have a response time requirement which is monitored. The following results have passed the response time requirements. The host hardware: A 2 socket, 8 core Nehalem with SMT, and EPT enabled, lots of disks, 4 x 1 GB Ethenret The host software: Both Xen and KVM use the same host Linux OS, SLES11. KVM uses the 2.6.27.19-5-default kernel and Xen uses the 2.6.27.19-5-xen kernel. I have tried 2.6.29 for KVM, but results are actually worse. KVM modules are rebuilt with kvm-85. Qemu is also from kvm-85. Xen version is "3.3.1_18546_12-3.1". The guest software: All guests are RedHat 5.3. The same disk images are used but different kernels. Xen uses the RedHat Xen kernel and KVM uses 2.6.29 with all paravirt build options enabled. Both use PV I/O drivers. Software used: Apache, PHP, Java, Glassfish, Postgresql, and Dovecot. Hypervisor configurations: Xen guests use "phy:" for disks KVM guests use "-drive" for disks with cache=none KVM guests are backed with large pages Memory and CPU sizings are different for each guest type, but a particular guest's sizings are the same for Xen and KVM The test run configuration: There are 4 sets of servers used, so that's 24 guests total (4 idle ones, 20 active ones). Test Results: The throughput is equal in these tests, as the clients throttle the work (this is assuming you don't run out of a resource on the host). What's telling is the CPU used to do the same amount of work: Xen: 52.85% KVM: 66.93% So, KVM requires 66.93/52.85 = 26.6% more CPU to do the same amount of work. Here's the breakdown: total user nice system irq softirq guest 66.90 7.20 0.00 12.94 0.35 3.39 43.02 Comparing guest time to all other busy time, that's a 23.88/43.02 = 55% overhead for virtualization. I certainly don't expect it to be 0, but 55% seems a bit high. So, what's the reason for this overhead? At the bottom is oprofile output of top functions for KVM. Some observations: 1) I'm seeing about 2.3% in scheduler functions [that I recognize]. Does that seems a bit excessive? 2) cpu_physical_memory_rw due to not using preadv/pwritev? 3) vmx_[save|load]_host_state: I take it this is from guest switches? We have 180,000 context switches a second. Is this more than expected? I wonder if schedstats can show why we context switch (need to let someone else run, yielded, waiting on io, etc). samples % name app 385914891 61.3122 kvm-intel.ko vmx_vcpu_run 11413793 1.8134 libc-2.9.so /lib64/libc-2.9.so 8943054 1.4208 qemu-system-x86_64 cpu_physical_memory_rw 6877593 1.0927 kvm.ko kvm_arch_vcpu_ioctl_run 6469799 1.0279 qemu-system-x86_64 phys_page_find_alloc 5080474 0.8072 vmlinux-2.6.27.19-5-default copy_user_generic_string 4154467 0.6600 kvm-intel.ko __vmx_load_host_state 3991060 0.6341 vmlinux-2.6.27.19-5-default schedule 3455331 0.5490 kvm-intel.ko vmx_save_host_state 2582344 0.4103 vmlinux-2.6.27.19-5-default find_busiest_group 2509543 0.3987 qemu-system-x86_64 main_loop_wait 2457476 0.3904 vmlinux-2.6.27.19-5-default kfree 2395296 0.3806 kvm.ko kvm_set_irq 2385298 0.3790 vmlinux-2.6.27.19-5-default fget_light 2229755 0.3543 vmlinux-2.6.27.19-5-default __switch_to 2178739 0.3461 bnx2.ko bnx2_rx_int 2156418 0.3426 vmlinux-2.6.27.19-5-default complete_signal 1854497 0.2946 qemu-system-x86_64 virtqueue_get_head 1833823 0.2913 vmlinux-2.6.27.19-5-default try_to_wake_up 1816954 0.2887 qemu-system-x86_64 cpu_physical_memory_map 1776548 0.2822 oprofiled find_kernel_image 1737294 0.2760 vmlinux-2.6.27.19-5-default kmem_cache_alloc 1662346 0.2641 qemu-system-x86_64 virtqueue_avail_bytes 1651070 0.2623 vmlinux-2.6.27.19-5-default do_select 1643139 0.2611 vmlinux-2.6.27.19-5-default update_curr 1640495 0.2606 vmlinux-2.6.27.19-5-default kmem_cache_free 1606493 0.2552 libpthread-2.9.so pthread_mutex_lock 1549536 0.2462 qemu-system-x86_64 lduw_phys 1535539 0.2440 vmlinux-2.6.27.19-5-default tg_shares_up 1438468 0.2285 vmlinux-2.6.27.19-5-default mwait_idle 1316461 0.2092 vmlinux-2.6.27.19-5-default __down_read 1282486 0.2038 vmlinux-2.6.27.19-5-default native_read_tsc 1226069 0.1948 oprofiled odb_update_node 1224551 0.1946 vmlinux-2.6.27.19-5-default sched_clock_cpu 1222684 0.1943 tun.ko tun_chr_aio_read 1194034 0.1897 vmlinux-2.6.27.19-5-default task_rq_lock 1186129 0.1884 kvm.ko x86_decode_insn 1131644 0.1798 bnx2.ko bnx2_start_xmit 1115575 0.1772 vmlinux-2.6.27.19-5-default enqueue_hrtimer 1044329 0.1659 vmlinux-2.6.27.19-5-default native_sched_clock 988546 0.1571 vmlinux-2.6.27.19-5-default fput 980615 0.1558 vmlinux-2.6.27.19-5-default __up_read 942270 0.1497 qemu-system-x86_64 kvm_run 925076 0.1470 kvm-intel.ko vmcs_writel 889220 0.1413 vmlinux-2.6.27.19-5-default dev_queue_xmit 884786 0.1406 kvm.ko kvm_apic_has_interrupt 880421 0.1399 librt-2.9.so /lib64/librt-2.9.so 880306 0.1399 vmlinux-2.6.27.19-5-default nf_iterate -Andrew Theurer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
