Long ago I started keeping my notes and a bit of editorial content on idle power consumption for various computers and related here:
http://saf.bio.caltech.edu/saving_power.html A few days ago I realized that there was no Intel Core information in there. Since I don't have any myself, I hunted down an iMac and a PC and found much to my surprise, that while the Core processors were quite efficient when idling, there was apparently no way to adjust the power consumption downward any further via Enhanced Speed Step (or whatever Intel calls it today.) I assume that the CPUs in these two boxes supported this capability, but the BIOS (or it's equivalent on a Mac) apparently didn't enable this feature. Sure it's a small sample, but in this day and age I really expected it to be enabled by default pretty much everywhere. Anyway, that got me thinking about idle power consumption on clusters. Many of you have machines that run at 100% CPU 24/7, and for those systems the following discussion is irrelevant. But there are other clusters around that tend to sit for long periods of time between jobs, and whatever power they are using while waiting for a job is pretty close to a total waste. This is even more common on regular PCs, where CPU usage is extremely "bursty". The thing is, on pretty much every machine I've seen (exception: some laptops) there is a gaping hole between the lowest power level on a running machine, and the power level when it goes to sleep. Putting idle nodes all the way to sleep would save the most power, but it is a nightmare in terms of waking them back up again. Besides the issue of disks that might not spin back up, there is the problem of the (many) network protocols which are going to time out and break connections. Also returning from sleep nodes tends to be relatively slow, taking many seconds to many minutes, depending on a whole lot of variables. So it would be nice if the range of underclocking / undervolting adjustments provided on compute nodes extended quite a bit further towards the lower end than it currently does. Typically idle is something like 70-80W at the lowest clock speed and sleep is 2-4W. There's a lot of room in there to work with. Why is there not a system that can slow down far enough to use only 15W and still run, albeit very slowly? On a diskless node 7-10W might even be possible. Machines running in these nodes would be alive enough to keep network connections open, and would be a whole lot easier to get back up to full speed than the equivalent machine in a sleep state. Assuming the transition speed is similar to Cool'N Quiet we're talking much less than a second to speed back up again. There are a lot of articles around about statically underclocked machines, which proves that running modern hardware slowly is possible, but the statically underclocked machines cannot be sped up again - they start slow, and stay slow. Via sells some processors like the C7 which will operate over a very wide power range, but unfortunately the fastest those will crunch isn't anywhere near the speed of an Opteron or Core. Big iron SMP machines often the ability to shut off CPUs while the machine is running, well, except for the last one obviously. With quad cores pretty much here, and octo cores on the horizon, one might imagine large power savings at idle could be achieved the same way on these chips. Can any of the high core number Opterons or Core CPUs power down unused cores now? In closing, does anybody currently make a rack mountable compute node with a really, really, really, low idle power mode, and also competitive performance when running at 100%? Regards, David Mathog [EMAIL PROTECTED] Manager, Sequence Analysis Facility, Biology Division, Caltech _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
