UNDERSTANDING PERFORMANCE MONITOR FOR AUTOCAD WHITE PAPER OCTOBER 21, 2010 Performance Monitor for AutoCAD The AutoCAD Performance Monitor (Labs release) is a Windows 7 or Vista sidebar gadget that measures virtual memory used by each running AutoCAD-based application (for example AutoCAD, AutoCAD Map 3D, and AutoCAD Civil 3D). When virtual memory threshold limits are exceeded, the monitor goes into warning (yellow) or alarm (red) to alert users to save files or tweak system variables before performing a memory-intensive operation that might cause the application to crash. This gadget is most useful on 32-bit systems, where some programs are pushing memory limits. With 64-bit systems, the virtual memory is so large that any thrashing or crashing is likely due to factors other than an out-of-memory condition. What is virtual memory? Virtual memory is the method of extending the available physical memory (random-access memory or RAM) by writing temporarily to the hard disk. If your computer lacks the RAM needed to run an operation, Windows uses virtual memory to compensate. When RAM runs low, virtual memory moves data from RAM to a space called a paging file or swapfile. Moving data to and from the paging file frees up RAM to complete its work. The total amount of memory available to programs is the amount of physical memory in the computer as well as the size of the pagefile. With swapping, the system divides memory into units called pages. Recently referenced pages are located in RAM. If a page of memory is not referenced for a while, it is written to the pagefile. This is called "swapping" or "paging out" memory. If that piece of memory is then later referenced by a program, the operating system reads the memory page back from the pagefile into physical memory, also called "swapping" or "paging in" memory. When the system is spending a lot of time loading and switching between processes, it can lead to a condition called thrashing, when all the processor s efforts are spent merely loading and switching between threads. Windows sets the initial minimum size of the paging file at the amount of RAM installed on your computer plus 300 MB, and the maximum size at 3 times the amount of RAM. Often the maximum RAM is less than the amount needed for all running programs, especially when multiple processes or applications execute simultaneously. That s why the solution is for programs to store some of their data on the hard drive and copy it back and forth to RAM as needed. As Eric Lippert states in his article Out Of Memory Does Not Refer to Physical Memory: An out of memory error almost never happens because there s not enough storage available; as we ve seen, storage is disk space, and disks are huge these days. Rather, an out of memory error happens because the process is unable to find a large enough section of contiguous unused pages in its virtual address space to do the requested mapping. out of memory errors usually have nothing to do with how much physical memory you have, or how even how much storage is available. It s almost always about the address space, which on 32 bit Windows is relatively small 1
and easily fragmented. And of course, many of these problems effectively go away on 64 bit Windows, where the address space is billions of times larger and therefore much harder to fragment. (The problem of thrashing of course still occurs if physical memory is smaller than total working set, no matter how big the address space gets.) Microsoft 32-bit and 64-bit Windows frequently asked questions Until recently, almost all consumer PCs used 32-bit processors. The bit size of a processor refers to the size of the address space it can reference. A 32-bit processor can reference 2^32 bytes, or 4 GB of memory, although only half is user-accessible (2 GB) while the other half is reserved for system processes. These 32-bit processors were standard at a time when 4 GB was thought to be more than enough memory space for Windows applications. Modern computing systems increasingly confront the 4 GB ceiling, because of memory-intensive applications that need to store multiple processes in memory simultaneously. Read more at A Closer Look at 32-Bit vs. 64-Bit Windows. When 64-bit architecture became available on consumer PCs, it resolved most memory issues. What s the difference between 32-bit and 64-bit memory management? Here are Microsoft s statistics: Memory type Description 32-bit limit 64-bit limit Virtual memory Method of extending the available physical memory (RAM) by writing to disk 4 GB (2GB for an application) 16 TB (8 TB for an application) Paging file size Disk file that the computer uses to increase the 16 TB 256 TB amount of physical storage for virtual memory Paged pool Region of virtual memory in system space that can be paged in and out of the working set of the system process Limited by kernel mode virtual address space 128 GB Non-paged pool Memory pool that consists of ranges of system virtual addresses that are guaranteed to be resident in physical memory at all times and thus can be accessed from any address space without incurring paging input/output Memory limits for different Windows releases are here and here. Limited by kernel mode virtual address space and physical memory 128 GB 2
Comparing Autodesk Performance Monitor to Windows task managers Windows Task Manager monitors the following physical memory metrics: Windows 7 Task Manager Memory item Working Set Private Working Set Peak Working Set Working Set Delta Commit Size Paged Pool Non-paged Pool Description Amount of memory in the private working set plus the amount of memory the process is using that can be shared by other processes. Subset of working set that specifically describes the amount of memory a process is using that can't be shared by other processes. Maximum amount of working set memory used by the process. Amount of change in working set memory used by the process. Amount of virtual memory that's reserved for use by a process. Amount of pageable memory (that which can be written to another storage medium, such as the hard disk). Amount of non-pageable memory (that which can't be written to another storage medium). 3
Windows 7 Resource Monitor The working set is the one most commonly tracked with Windows monitors. Note that the working set is for RAM only and graphs usually combine all running processes for all applications. So when you re looking at Windows Task Manager or Resource Monitor, you re not seeing virtual memory nor are you seeing individual AutoCAD processes separated in the graphs. If one were to measure just the working set, as does Windows Task Manager, here are the misleading issues that could occur: Physical memory is dynamically allocated by the operating system. If you ve opened many other applications besides AutoCAD and the latter has used up almost all the 4G virtual memory, its working set could still be small because all the other processes are consuming it. However, AutoCAD could still crash because it is approaching virtual memory limits, but none of this would show up on a monitor tracking only working set. Low working set usage doesn t mean the process always has good performance. Sometimes the working set could be small, but the application is slow. With conventional metrics, you have no other way to see that the virtual memory is being consumed. So, restricting monitoring to RAM s working set is not so helpful with out-of-memory errors. 4
Comparing Autodesk Performance Monitor to Windows (Reliability and) Performance Monitor Both Windows 7 and Vista have another performance monitor available on your system. It s called the Reliability and Performance Monitor under Vista and Performance Monitor under Windows 7. You can access it through Control Panel > Performance Information and Tools > Advanced tools > Open Performance Monitor, and then selecting Performance Monitor from the tree. Or you can type perfmon from the Run command window. Here you see the Windows monitor (on the left) with the metrics (called counters ) set up to match the Autodesk Performance Monitor. The key metric is Virtual Bytes, which is under the Process category. If you select only the acad instance of this counter, you ll see the same measurement that Autodesk s gadget uses for the In Use value. The example here displays the Windows monitor Virtual Bytes in red, Working Set in dark blue, and Page File Bytes in light blue. This is on a 64-bit system. You can see that the virtual bytes in use are 2,835,596,247 bytes, which corresponds to the 2747 MB value shown in the Autodesk monitor. Note also that the 8,388,607 MB total available virtual memory for the Autodesk gadget corresponds to the 8 TB available for each application on 64-bit systems. So, you can use the Windows Performance Monitor to track the same metrics that the Autodesk gadget does, but the added value with the Autodesk gadget is that you can set warning thresholds and see the settings of the AutoCAD files and applications running. 5
See below for an illustration of how to set up virtual memory in the Windows Performance Monitor. Adding "counters" to Windows Performance Monitor to view specialized processes When should you use Performance Monitor for AutoCAD? If you have a 32-bit system running on Windows 7 or Vista and it has been thrashing or crashing with out-of-memory errors, then this gadget could be useful to you. It not only isolates the virtual memory metrics (which are not readily available in standard monitors), it also shows some useful information about the AutoCAD files open. Filling up virtual memory is what can cause instability in 32-bit AutoCAD. Getting notified gives you time to save a file or do some other tweaking before AutoCAD crashes. The settings panel allows you to set warning and error threshold limits. When the virtual memory reaches these thresholds, the status turns yellow or red, and you could do some safety operations such as closing some drawings to reduce virtual memory usage. Of course, in 64-bit computers, the virtual memory is very large, so this gadget may not be as useful. However, even 64-bit AutoCAD could run out of virtual memory, especially if the program needs more memory management tuning or if the working set grows larger than the physical RAM available. 6
Known issues with the Labs release of Performance Monitor for AutoCAD When the computer is thrashing extensively, the Performance Monitor status bar does not update with color, even though it has passed the yellow or red alarm thresholds. The text inside the flyout panel turns color, but the meter bar does not correspond. When AutoCAD is busy in a process, it denies access for querying, so the gadget turns gray and cannot display current status. Normally the gadget refreshes its main page every 10 seconds. So you should check the status of the system before you initiate large memory-intensive processes, such as starting a plot with multiple layouts, importing large orthoimagery or point cloud files, or building a large Civil 3D surface. Note that the 64-bit version measures such a vast amount of virtual memory that the gadget is at.02% In Use and doesn t register a meter bar. You may find that any 64-bit crashes are not for out-of-memory issues and so the gadget will not be help to you. Note that the gadget works with only Windows 7 and Vista and is not supported on Windows XP. Please send feedback on the Performance Monitor for AutoCAD and on this white paper to the Autodesk Discussion Groups, labs.acad.perfmon@autodesk.com, or It s Alive in the Lab. Autodesk and AutoCAD are either registered trademarks or trademarks of Autodesk, Inc., in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product offerings and specifications at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document. 2010 Autodesk, Inc. All rights reserved. 7