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178 • Linux Symposium 2004 • Volume One pstates. Rules are used to dynamically choose which profile to use, and my rules are setup to transition profiles based on total processor load. My simple configuration file to change processor frequency dependent on system load is: [General] pidfile=/var/run/cpufreqd.pid poll_interval=2 pm_type=acpi # 2.2 GHz processor speed [Profile] name=hi_boost minfreq=95% maxfreq=100% policy=performance # 2.0 GHz processor speed [Profile] name=medium_boost minfreq=90% maxfreq=93% policy=performance # 1.0 GHz processor Speed [Profile] name=lo_boost minfreq=40% maxfreq=50% policy=powersave [Profile] name=lo_power minfreq=40% maxfreq=50% policy=powersave [Rule] #not busy 0%-40% name=conservative ac=on battery_interval=0-100 cpu_interval=0-40 profile=lo_boost #medium busy 30%-80% [Rule] name=lo_cpu_boost ac=on battery_interval=0-100 cpu_interval=30-80 profile=medium_boost #really busy 70%-100% [Rule] name=hi_cpu_boost ac=on battery_interval=50-100 cpu_interval=70-100 profile=hi_boost This approach actually works very well for multiple small tasks, for transitioning the frequencies of all the processors together based on a collective loading statistic. For a long running, single threaded task, this approach does not work well as the load is only high on a single processor, with the others being idle. The average load is thus low, and all processors are kept at a slow speed. Such a workload scenario would require an implementation that looked at the loading of individual processors, rather than the average. See the section below on future work. 8.4 The Drivers Involved powernow-k8.ko arch/i386/ kernel/cpu/cpufreq/powernow-k8. c (the same source code is built as a 32-bit driver in the i386 tree and as a 64-bit driver in the x86_64 tree) drivers/acpi drivers/cpufreq
Linux Symposium 2004 • Volume One • 179 The Test Driver Note that the powernow-k8.ko driver does not export any read, write, or ioctl interfaces. For test purposes, a second driver exists with an ioctl interface for test application use. The test driver was a big part of the test effort on powernow-k8.ko prior to release. 8.5 Frequency Driver Entry Points powernowk8_init() Driver late_initcall. Initialization is late as the acpi driver needs to be initialized first. Verifies that all processors in the system are capable of frequency transitions, and that all processors are supported processors. Builds a data structure with the addresses of the four entry points for cpufreq use (listed below), and calls cpufreq_register_driver(). powernowk8_exit() Called when the driver is to be unloaded. Calls cpufreq_unregister_driver(). 8.6 Frequency Driver Entry Points For Use By The CPUFreq driver powernowk8_cpu_init() This is a per-processor initialization routine. As we are not guaranteed to be executing on the processor in question, and as the driver needs access to MSRs, the driver needs to force itself to run on the correct processor by using set_cpus_allowed(). This pre-processor initialization allows for processors to be taken offline or brought online dynamically. I.e., this is part of the software support that would be needed for processor hotplug, although this is not supported in the hardware. This routine finds the ACPI pstate data for this processor, and extracts the (proprietary) data from the ACPI _PSS objects. This data is verified as far as is reasonable. Per-processor data tables for use during frequency transitions are constructed from this information. powernowk8_cpu_exit() Per-processor cleanup routine. powernowk8_verify() When the root user (or an application running on behalf of the root user) requests a change to the minimum/maximum frequencies, or to the policy or governor, the frequency driver’s verification routine is called to verify (and correct if necessary) the input values. For example, if the maximum speed of the processor is 2.4 GHz and the user requests that the maximum range be set to 3.0 GHz, the verify routine will correct the maximum value to a value that is actually possible. The user can, however, chose a value that is less than the hardware maximum, for example 2.0 GHz in this case. As this routine just needs to access the perprocessor data, and not any MSRs, it does not matter which processor executes this code. powernowk8_target() This is the driver entry point that actually performs a transition to a new frequency/voltage. This entry point is called for each processor that needs to transition to a new frequency. There is therefore an optimization possible by enhancing the interface between the frequency driver and the CPUFreq driver for the case where all processors are to be transitioned to a new, common frequency. However, it is not clear that such an optimization is worth the complexity, as the functionality to transition a single processor would still be needed. This routine is invoked with the processor
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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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