On Tue, 12 Aug 2008 21:03:02 +0200 Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> wrote: > Hi Arjan, > > On Mon, Aug 11, 2008 at 04:58:16PM -0700, Arjan van de Ven wrote: > > > Hi, > > > > > > On Mon, Aug 11, 2008 at 07:11:28AM -0700, Arjan van de Ven wrote: > > > > 1) when the cpu is idle (as in "idle loop C states/hlt"; > > > > p4_clockmod doesn't mean anything.. the clock is stopped not > > > > just skipped. 2) when the cpu is executing code (eg non-idle), > > > > it takes more power for a unit of time than it takes when it's > > > > idle > > > > > > This statement might be true, but might also be wrong: > > > a) on systems where only C1 is exported, p4-clockmod most > > > often equals the state the CPU is in when in C1[*], > > > > that's.. not entirely true btw. > > well, the spec isn't really clear about this. It says (IA32 Intel > Architecture Software Developer's Manual, Volume 3, section 13.14.3) > that P6 family processors did this using STPCLK#. And STPCLK# was > also used by the chipset to force the CPU to enter C2, IIRC. not quite.. if it does for a certain cpu, then it's only for cpus that support C2. > Do P4s only do an C1-equivalent (or even less than that) now, as they > do the thermal throttling internally instead of externally using > STPCLK#? it's basically always less (or really best case equal) than c1 just due to the really short duration > > If it's C2-equivalent vs. C1, it's a win. it's not. >So throttling would be a > win from this perspective on a only C1-capable PIII, but not on a P4? > Is that what you're trying to hint at here? not even on PIII is it a win.. it's just too short a duration and your C2 theory.. not sure I believe it. > > To summarize: > > (1) p6 family processors use STPCLK# initiated by the chipset for > thermal throttling. > (2) STPCLK# is also used by the chipset to make the CPU enter C2. well.... sometimes. It's more complex generally. > (3) p4-clockmod uses the STPCLK#-equivalent in p4 CPUs. > (4) Therefore, it is as effective as STPCLK#, and as effective as C2. This is not correct. C2 is only effective if you stay in it "long enough". Otherwise you pay the transition cost twice. > (5) STPCLK#/C2 has higher energy savings than hlt/C1. incorrect -- If you want to reach me at my work email, use arjan@xxxxxxxxxxxxxxx For development, discussion and tips for power savings, visit http://www.lesswatts.org -- 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
