On Mon, 23 Nov 2009 20:26:53 +0100 Erik Slagter <erik@xxxxxxxxxxxx> wrote: > > No, that isn't normal. C-states on modern processors generally > > save a lot of energy. > > > > If you run powertop and you find that you are over 99% idle > > and you save no energy compared to when you are 0% idle > > (say a copy of "cat /dev/zero> /dev/null" for each core) > > then something is wrong with your system. > > I just removed a large story here, I guess the table from my other > message is a lot more informative. > > > It is possible, but as soon as you reverse engineer and over-ride > > something in the BIOS, you are on very thin ice. Presumably > > the BIOS engineer made a concious decision to disable C-states > > when you over-clock your board and had a reason to do so. > > As long as nothing gets fried that's no problem for me. > > > Maybe the more important question is what measurable benefit > > you get when you over-clock your board, and if you really need > > that... > > I can understand your doubts on this matter, but I think I do have a > legitimate reasoning. This is a server that almost all of the time > does next to nothing. Load 0.02 or similar. It needs to be running > 24/24 though because it receives e-mail and answers the telephone. So > that's why I want it to be low on power usage. On the other hand I > need to transcode movie clips to h264 very regularly. I can use every > 4*2 core for the process using x264 and indeed it works very fast. > Also I noticed that every mhz higher clock means shorter encoding > time, all (virtual-)cores get completely loaded. The "normal" speed > of the 920 is 2.8 Ghz (or in fact 2.63 Ghz) and a change to 3.4 Ghz > really does make a difference in encoding speed, theoretically 30%, > in practise even more. > > Intel would really make me happy if they would design a processor > with four or more cores and a chipset that would implement C7 and > also could scale from 100 Mhz to 3.6 Ghz, in two or three steps, I > wouldn't mind, and then would use something like 20 watts in idle, > like my laptop does. Most of the overclockers disable C3/C6/C7 anyway for stability reasons, probably because sudden changes in core voltage disturb the CPU operation. My i5 Lynnfield desktop was actually unusable with C3/C6/C7 even with default settings (fsck reporting random errors etc.). I ended up disabling the higher C-states and just raised the Base clock so I do not need the Turbo mode. As long as you do not disable C1, the difference in idle power consumption is rather small. -- Jindrich Makovicka -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
