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184 • Linux Symposium 2004 • Volume One checking of the ACPI provided data. The disadvantage of this is the need to update the database for new processor revisions. The advantages are the ability to overcome the ACPI imposed restrictions, and also to allow the use of the technology on systems where the ACPI support is not enabled. 14.2 Kernel Scheduler—CPU Power An enhanced scheduler for the 2.6 kernel (2.6.6-bk1) is aware of groups of processors with different processing power. The power tating of each CPU group should be dynamically adjusted using a cpufreq transition notifier as the processor frequencies are changed. See http://lwn.net/Articles/ 80601/ for a detailed acount of the scheduler changes. 14.3 Thermal Management, ACPI Thermal Zones Publicly available BIOSs for AMD machines do not implement thermal zones. Obviously this is one way to provide the input control for frequency management based on thermal conditions. 14.4 Thermal Management, Service Processor Servers typically have a service processor, which may be compliant to the IPMI specification. This service processor is able to accurately monitor temperature at different locations within the chassis. The 2.6 kernel includes an IPMI driver. User space code may use these thermal readings to control fan speeds and generate administrator alerts. It may make sense to also use these accurate thermal readings to trigger frequency transitions. The interaction between thermal events from the service processor and ACPI thermal zones may be a problem. Hiding Thermal Conditions One concern with the use of CPU frequency manipulation to avoid overheating is that hardware problems may not be noticed. Over temperature conditions would normally cause administrator alerts, but if the processor is first taken to a lower frequency to hold temperature down, then the alert may not be generated. A failing fan (not spinning at full speed) could therefore be missed. Some hardware components fail gradually, and early warning of imminent failures is needed to perform planned maintenance. Losing this data would be badness. 15 Legal Information Copyright © 2004 Advanced Micro Devices, Inc Permission to redistribute in accordance with Linux Symposium submission guidelines is granted; all other rights reserved. AMD, the AMD Arrow logo, AMD Opteron, AMD Athlon and combinations thereof, AMD- 8111, AMD-8131, and AMD-8151 are trademarks of Advanced Micro Devices, Inc. Linux is a registered trademark of Linus Torvalds. HyperTransport is a licensed trademark of the HyperTransport Technology Consortium. Other product names used in this publication are for identification purposes only and may be trademarks of their respective companies. 16 References 1. AMD Opteron Processor Data Sheet, publication 23932, available from www. amd.com 2. AMD Opteron Processor Power And
Linux Symposium 2004 • Volume One • 185 Thermal Data Sheet, publication 30417, available from www.amd.com 3. AMD Athlon 64 Processor Power And Thermal Data Sheet, publication 30430, available from www.amd.com 4. BIOS and Kernel Developer’s Guide (the BKDG) for AMD Athlon 64 and AMD Opteron Processors, publication 26094, available from www.amd.com. Chapter 9 covers frequency management. 5. ACPI 2.0b Specification, from www. acpi.info 6. Text documentation files in the kernel linux/Documentation/cpu-freq/ directory: • index.txt • user-guide.txt • core.txt • cpu-drivers.txt • governors.txt
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Proceedings of the Linux Symposium
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The State of ACPI in the Linux Kern
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Conference Organizers Andrew J. Hut
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TCP Connection Passing Werner Almes
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Linux Symposium 2004 • Volume One
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Cooperative Linux Dan Aloni da-x@co
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Build your own Wireless Access Poin
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Run-time testing of LSB Application
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Linux Block IO—present and future
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Linux AIO Performance and Robustnes
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Methods to Improve Bootup Time in L
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Linux on NUMA Systems Martin J. Bli
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Improving Kernel Performance by Unm
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Linux Virtualization on IBM POWER5
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The State of ACPI in the Linux Kern
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IA64-Linux perf tools for IO dorks
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Carrier Grade Server Features in th
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Demands, Solutions, and Improvement
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Hotplug Memory and the Linux VM Dav
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