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170 • Linux Symposium 2004 • Volume One 5 Interesting Scenarios These are real world scenarios, where the application of the technology is appropriate. 5.1 Save power in an idle cluster A cluster would typically be kept running at all times, allowing remote access on demand. During the periods when the cluster is idle, reducing the CPU frequency is a good way to reduce power consumption (and therefore also air conditioning load), yet be able to quickly transition back up to full speed (
Linux Symposium 2004 • Volume One • 171 demanding case is a blade server) aggravates the cooling problem as the neighboring boxes are also generating heat. 6 System Power Budget The processors are only part of the system. We therefore need to understand the power consumption of the entire system to see how significant processor frequency management is on the power consumption of the whole system. A system power budget is obviously platform specific. This sample DC (direct current) power budget is for a 4-processor AMD Opteron processor based system. The system has three 500W power supplies, of which one is redundant. Analysis shows that for many operating scenarios, the system could run on a single power supply. This analysis is of DC power. For the system in question, the efficiency of the power supplies are approximately linear across varying loads, and thus the DC power figures expressed as percentages are meaningful as predictors of the AC (alternating current) power consumption. For systems with power supplies that are not linearly efficient across varying loads, the calculations obviously have to be factored to take account of power supply efficiency. System components: • 4 processors @ 89W = 356W in the maximum pstate, 4 @ 22W = 88W in the minimum pstate. These are worst case figures, at maximium case temperature, with the worst case instruction mix. The figures in Table1 are reduced from these maximums by approximately 10% to account for a reduced case temperature and for a workload that does not keep all of the processors’ internal units busy. • Two disk drives (Western Digital 250 GByte SATA), 16W read/write, 10W idle (spinning), 1.3W sleep (not spinning). Note SCSI drives typically consume more power. • DVD Drive, 10W read, 1W idle/sleep. • PCI 2.2 Slots – absolute max of 25W per slot, system will have a total power budget that may not account for maximum power in all slots. Estimate 2 slots occupied at a total of 20W. • VGA video card in a PCI slot. 5W. (AGP would be more like 15W+). • DDR DRAM, 10W max per DIMM, 40W for 4 GBytes configured as 4 DIMMs. • Network (built in) 5W. • Motherboard and components 30W. • 10 fans @ 6W each. 60W. • Keyboard + Mouse 3W See Table 1 for the sample power budget under busy and light loads. The light load without any frequency reduction is baselined as 100%. The power consumption is shown for the same light load with frequency reduction enabled, and again where the idle loop incorporates the hlt instruction. Using frequency management, the power consumption drops to 43%, and adding the use of the hlt instruction (assuming 50% time halted), the power consumption drops further to 33%. These are significant power savings, for systems that are under light load conditions at times. The percentage of time that the system is running under reduced load has to be known to predict actual power savings.
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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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Linux AIO Performance and Robustnes
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