tiago wrote: > ---------- Forwarded message ---------- > From: Tiago Marques <tiago...@gmail.com> > Date: Sat, May 8, 2010 at 12:17 PM > Subject: Re: XO 1.5 frequency scaling > To: "Richard A. Smith" <rich...@laptop.org> > > > Hi Richard, > > On Wed, May 5, 2010 at 12:28 AM, Richard A. Smith <rich...@laptop.org>wrote: > > > On 05/04/2010 07:01 PM, Tiago Marques wrote: > > > > > Let me see if I understand what you said. I understand how it works on > > > desktop and regular laptops. You load the module for the specific power > > > saving feature and either a kernel module to do the job or the userspace > > > module which then allows a daemon to do the frequency scaling. > > > Now the XO 1.5, AFAIK, isn't doing it or powerd is doing it(or openfw). > > > I tried loading the C7 power saver module but it can't find the device. > > > Is it already being taken and should I not worry with frequency scaling > > > although /proc/cpuinfo always shows 1000MHz? > > > > The module is not enabled in the kernel build and in our case appears to > > only offer saving in very limited cases. Yes, you could cap your max > > frequency and max power draw but in general you end up using more > > power*time that way because you keep all the other components that don't > > have sort of power scaling up longer then they would have been because > > it takes longer to do the task. If you decrease the power draw 2x but > > then extend the time 2x you have gained nothing. > > > > > Not my experience, but I'm desktop biased I guess. I was thinking that you > could further lower the core voltage on the XO and get something like 50% > the clock with 25% or less power. But, as you describe below, if VIA managed > such an agressive power gating, it's the way to go. > > > > Feel free to experiment though. The latest versions of powerd have > > power logging built in and if you want a more specific measurement my > > power logging scripts should be useful. > > > > IIRC I had to hack on the driver a bit to make it work. The following > > is a summary email I posted from when I worked on it. > > > > Notes: > > - Ignore the comment about C5. Our CPU does not support C5. > > > > - Ignore the comment about being scared to burn up the CPU. We now have > > thermal throttling enabled and have tested it extensively. Unless you > > turn that off you should not be able to burn up the CPU. > > > > This is on olpc-powerd or the VIA C7 powersaver driver? I couldn't find > anything related to over/underclocking in powerd.
you're right. there's nothing in powerd related to clocking. powerd limits itself to managing the display, wlan on/off, and system suspend. > Did I miss some firmware or kernel update, as I can't load the c7 powersaver > kernel module in a kernel I built myself. are you sure you're running the kernel you built? (i.e., it, and whatever symlinks it needs to vmlinuz, need to be in /boot and /bootpart/boot.) paul > > > > > > ====================== > > I spent the day/night today working on getting our C states and P states > > enabled. > > > > The good news is that I got C4,C5 and frequency/voltage scaling (P > > states) working. > > > > The bad news is that C5 causes memory corruption and P states don't help > > much. > > > > Enabling C4 seems to save us about 170mW in idle. > > > > Any measurement on how low it goes in C4? > > > > > > C5 should save us a bit more but with it enabled the system won't boot. > > It gets all sorts of funky ext4 errors. C5 turns off the L2 cache and > > the docs say you should flush before entering. I suspect thats not > > happening. > > > > P states currently don't seem to save us enough to be measured. One > > reason is that our core voltage is set by default to be very close to > > the minimum. Its at .796V and the minimum is .7V with scaling enabled > > (+ code hack) the minimum setting drops Vcore to .73V. Its supposed to > > go to .7 but the volt meter says otherwise. 60mV diff doesn't offer a > > whole lot of savings. > > > > I see, I thought they could drop it even further. > > > > > > The CPU frequency slides between 400Mhz and 1GHz and you would think > > that it would make a large difference but the meter says otherwise. How > > can that be you ask? The answer is because Linux issues a hlt when > > idle. If you run the test under OFW then you can create up to 1.5W of > > power difference by sliding the freq from min to max [1] and holding the > > Vcore constant. But in idle not so much. The processor already does a > > very good job of gating the clocks. > > > > > Nice, kudos for VIA. > > > > So this brings us back to what we already knew. The big money on power > > savings is in our special sauce idle suspend. > > > > [1] Turns out you can overclock the processor. Via lists the max > > multiplier at 16x FSB (100Mhz) which is 1.6Ghz even though its listed as > > a max of 1Ghz. However if you continue to put values into the multiplier > > register the power draw continues to increase. I stopped when the > > system draw had hit 9W cause the XO on the power meter does not have a > > heat spreader and I didn't want to take the chance of burning it up. > > ================= > > > > The heatspreader I can hack with a heatpipe and some coolers, I'm going to > do it anyway since it is already going to 85ºC in load. The speed is of some > use to me most of the time, I'm just worried that the VRM can't handle the > extra current. > > Best regards, > Tiago > > > > > > -- > > > > Richard A. Smith <rich...@laptop.org> > > One Laptop per Child > > _______________________________________________ > > Devel mailing list > > Devel@lists.laptop.org > > http://lists.laptop.org/listinfo/devel > > > part 2 text/plain 129 > _______________________________________________ > Devel mailing list > Devel@lists.laptop.org > http://lists.laptop.org/listinfo/devel =--------------------- paul fox, p...@laptop.org
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