Troubleshooting Performance Issues in a Citrix Virtualized Environment

1. Troubleshooting Performance Issues in a Citrix Virtualized Environment Kapil Ramlal Sr. Software Maintenance Engineer Daniel Lazar Lead Escalation Engineer

2. Agenda • XenServer Performance Overview • Troubleshooting XenServer Performance • Windows Application Architecture Primer • Troubleshooting Virtual Machine Performance • Citrix Performance VM Demo • Q & A Citrix Confidential - Do Not Distribute

3. XenServer Performance Overview

4. XenServer Performance Overview XenServer is designed to do one thing… Performance is a function of “VM density” All hypervisors have VM density limitations Citrix XenServer …Consolidate machine workloads Citrix Confidential - Do Not Distribute

5. XenServer Performance Overview How do we determine optimal VM density for a host? XenServer Hardware Infrastructure, such as network and storage Workload and sizing demands of the virtual machines Native XenServer characteristics Citrix Confidential - Do Not Distribute

6. Dom0 DomU DomU Toolstack App App App App Guest OS Guest OS netback netfront netfront Native Driver Xen Hypervisor Host Machine (Hardware)

7. XenServer Performance Overview External Factors Network Storage VM Workload and Sizing Citrix Confidential - Do Not Distribute

8. Troubleshooting XenServer Performance

9. Domain 0 Memory Management for Dom0 for DomU total Dom0 = memory required for n VMs ( 6 MB x n 352 MB 400 MB 346 MB 752 MB 6 MB ) 328 MB 6 MB 6 MB 6 MB for DomU + = Total DomU “footprint” for DomU Total XenServer Memory Pool (ex. 12GB) Dom0 Memory Pool for DomU 752MB allows for about 60 VMs-per-host

10. Troubleshooting XenServer Performance • What happens when we start more VMs than Dom0 has memory to manage? • Slow VM performance, poor user experience. • Slow response from XenAPI—takes longer to process tasks like starting, shutting down and migrating virtual machines. • It can cause XenServer host instability resulting in unpredictable behavior and potentially crashing the XenServer host machine!! Citrix Confidential - Do Not Distribute

11. Troubleshooting XenServer Performance There are two common ways to monitor performance in XenServer XenServer Command Line Interface XenCenter Performance Tab Citrix Confidential - Do Not Distribute

12. Troubleshooting XenServer Performance Using XenCenter • Good for ‘at a glance’ monitoring • Unwieldy for refined or customized performance testing • Difficult to use for historical trending • Data cannot be easily exported • Some types of information not gathered. Citrix Confidential - Do Not Distribute

13. Troubleshooting XenServer Performance Performance monitoring commands # top # Provides a dynamic real-time view of a running system. Tasks: 68 total, 2 running, 65 sleeping, 0 stopped, 1 zombie Cpu(s): 13.0%us, 33.6%sy, 0.0%ni, 1.0%id, 52.5%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 417792k total, 302832k used, 114960k free, 68384k buffers Swap: 524280k total, 104k used, 524176k free, 80928k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 12857 65550 15 0 27784 3012 1280 D 19 0.6 0:00.57 qemu-dm 4679 root 12 -3 281m 16m 5308 S 12 3.4 3:47.85 xapi 5993 root 15 -3 6164 2276 1188 S 2 0.5 0:24.73 stunnel 1264 root 16 -4 2244 664 384 S 0 0.1 0:24.00 udevd 4641 root 15 0 16348 1936 952 S 0 0.4 0:01.25 xenstored 4650 root 15 0 12304 652 544 S 0 0.1 0:00.05 blktapctrl 12722 root 15 0 2188 1052 836 R 0 0.2 0:00.03 top Citrix Confidential - Do Not Distribute

14. Troubleshooting XenServer Performance Performance monitoring commands # xentop # Displays real-time information about a Xen system and domains. xentop - 17:24:33 Xen 3.3.1 4 domains: 1 running, 3 blocked, 0 paused, 0 crashed, 0 dying, 0 shutdown Mem: 12580820k total, 7092880k used, 5487940k free CPUs: 8 @ 1600MHz NAME STATE CPU(sec) CPU(%) MEM(k) MEM(%) MAXMEM(k) MAXMEM(%) VCPUS NETS ... Domain-0 -----r 9849 65.5 417792 3.9 no limit n/a 8 0 ... Win2K3-01 ------ 1 1.5 2097020 16.7 2106164 16.7 2 1 ... Win2K3-02 ------ 1 4.3 2097020 16.7 2106164 16.7 2 1 ... Win2K3-03 ------ 0 9.8 2097020 16.7 2106164 16.7 2 1 ... Citrix Confidential - Do Not Distribute

15. Troubleshooting XenServer Performance What if I need to increase my VM-density-per-host? We can tune XenServer to increase VM density. In a scalability study conducted by Citrix to determine the maximum number of Windows XP virtual desktops per host for XenServer 5.5 running XenDesktop 4 we were able to host 130 VMs per host. Citrix Confidential - Do Not Distribute

16. Troubleshooting XenServer Performance This was achieved by making two key configuration changes to a default XenServer 5.5 installation. • Increased the amount of RAM assigned to Dom0 to 2.94GB from the default 752MB; increasing it enabled us to launch more desktop clients. • Increased the “Xen-heap” setting to take into account the large number of VMs on this single server host. This was done by adding "xenheap_megabytes=24" to the Xen command-line in /boot/extlinux.conf which resulted in an increase from the default of 16MB to 24MB. Citrix Confidential - Do Not Distribute

17. Troubleshooting XenServer Performance Additional Information Both the scalability study and instructions for increasing Dom0 memory limits are documented in the Citrix Knowledge Center here: • http://support.citrix.com/article/CTX124086 - XenServer Single Server Scalability with XenDesktop • http://support.citrix.com/article/CTX124259 - Adjusting Dom0 and Xenheap Setting in XenServer Disclaimer: Your results may vary! This testing was done on very high-end equipment using Citrix best practices! Citrix Confidential - Do Not Distribute

18. Troubleshooting XenServer Performance Troubleshooting commands - Storage # iostat # Reports basic I/O stats for devices and partitions # hdparm # Performs timed sequential reads # dd # Simple, common block device copy utility TIP: iSCSI storage throughput can usually be tied directly to network performance. If there is slow throughput for an iSCSI storage array, perform network diagnostics first!! Citrix Confidential - Do Not Distribute

19. Troubleshooting XenServer Performance Troubleshooting commands - Network # tcpdump # Dumps traffic on a network • http://support.citrix.com/article/CTX120869 - detailed instructions for using tcpdump. # netstat # Display network interface statistics # ifconfig # Display and configure network interfaces TIP: You can always type ‘man’ followed by a Linux command name (i.e., ‘man netstat’) to get detailed help for the command. Citrix Confidential - Do Not Distribute

20. Troubleshooting XenServer Performance Running Shell Scripts • Can capture customized data sets • Can be run over defined periods of time • Can be formatted specifically for reporting purposes. • Requires knowledge of Linux and shell scripting languages. Citrix Confidential - Do Not Distribute

21. Troubleshooting XenServer Performance Additional Information On the Citrix Knowledge Center you can find shell script examples, procedures and best practices for how to troubleshoot all aspects of a XenServer environment. Some useful links to troubleshooting articles: • http://support.citrix.com/article/CTX124157 • http://support.citrix.com/article/CTX121634 • http://support.citrix.com/article/CTX122806 • http://support.citrix.com/article/CTX120737 Citrix Confidential - Do Not Distribute

22. Windows Application Architecture Primer

23. A process, in the simplest terms, is an executing program. - Microsoft (2010) Citrix Confidential - Do Not Distribute

24. Application Basics • An application consists of one or more processes • Each process provides the resources needed to execute a program • One or more threads run in the context of the process • Each process is started with a single thread, often called the primary thread, but can create additional threads

25. Application Basics • A thread is the basic unit to which the operating system allocates processor time • Threads carry out the work of aprocess • All threads of a process share its virtual address space and system resources • Uses stack-based storage for handling data What is a Thread?

26. Application Basics Thread Stack • What is the Stack? • It’s temporary memory used by threads • It’s used to store function’s parameters and Local variables Frame Pointer

27. A closer look Citrix Confidential - Do Not Distribute

29. Application Basics User & Kernel Space • The Windows operating system can be conceptually divided into 2 parts: • User Space (User Mode) • Kernel Space (Kernel Mode) • Applications run in User Mode • System drivers run in Kernel Mode (Privileged Mode)

30. USER SPACE USER APPLICATION USER APPLICATION USER MODE USER APPLICATION USER APPLICATION USER APPLICATION KERNEL SPACE rusb2w2k.sys keyboard.sys win32k.sys tcpip.sys […]

31. Troubleshooting Virtual Machine Performance

32. Troubleshooting Virtual Machine Performance • Common performance related issues inside the VM: • High CPU • Disk/registry contention • High network utilization • Memory

33. High CPU • Identify offending Thread (s) • Identify the top function call and its module • Capture user memory dump of offending process for analysis • Engage respective application vendor ProcessExplorer can be used for live stack-trace viewing!

34. The Windows Performance Tools • Next generation performance monitoring from Microsoft • Track CPU usage, application start times, boot issues etc. • Identify common performance problems without a debugger • Included with Windows 7 SDK Download

35. The Windows Performance Tools: Case Study ISSUE: • High CPU on wfica32.exe Methodology • Compare a 30-second sample of activity and compare to non-working ICA, working ICAand working RDP

36. The Windows Performance Tools: Case Study ICA test run where problem occurred • Notice that on this dual processor machine –1 processor is frequently at or very close to 100%. • Looking inside the above testing to see which instructions were being executed the most during the test –was wfica32.exe.

37. The Windows Performance Tools: Case Study • Drilling into the calls of wfica32.exe, lead to theWindows function NtUserSetCursor() which results in calls to theigdkmd32.sys driver and then into the kernel –specifically the memcpy()function.

38. Memory Dump Collection • User dumps contain a snapshot of a process’ memory • Kernel dumps contain a snapshot of kernel memory space • A complete memory dump contains both the kernel and the entire user space

39. User Dump Collection • Configure a default post-mortem debugger: How to Set the NT Symbolic Debugger as a Default Windows Postmortem Debugger(CTX105888) How to Set WinDbg as a Default Windows Postmortem Debugger (CTX107528) Use Task Manager for manual dumps

40. To enable a complete memory dump using the registry: Set the CrashDumpEnabled value to 1 HKLM\System\CurrentControlSet\Control\CrashControl System Dump Collection • Small Memory Dump • Generally we avoid • Kernel Memory Dump • System crash • Complete Memory Dump • System unresponsive Control Panel -> System->Advanced Tab -> Startup and Recovery

41. System Dump Collection • Windows 7 introduced the Dedicated Dump Drive setting • Allows a pagefile to be configured on a dedicated drive for dump capture • Recommended to debug VM’s streamed through PVS How to Recover Windows Kernel Level Dump Files from Provisioned Target (CTX123642) Citrix Confidential - Do Not Distribute

42. Demo: Citrix XenServer Performance VM

44. Q & A

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