From: Thomas Renninger <trenn@xxxxxxx> Date: Wed, Oct 13, 2010 at 05:17:18PM -0400 (adding Andreas, I'm sure he'd like to pitch in here too) Hi Thomas, > > > Possibly this can still be done and cpb can get marked deprecated > > > (it shows up in 2.6.36 the first time? Which is not released yet? > > > Theoretically this is not part of the ABI yet...). > > > > No, cpb got introduced in .35. > > > > And no, we don't want to remove it because we need to be able to toggle > > CPB without the need for installing a special tool for that. > Maybe not removing, but having a sysfs file for each cpu even you can > only enable/disable boost for the whole machine looks wrong. > Ok, there may be future machines where you could disable it per CPU socket?, > but what for... I see your point, having this file per-cpu is redundant since we do the boosting per system. And yes, I really don't have a sensible usecase where you might want to have a finer granularity with boost control, i.e. disable single cores only. > Also the dependency to powernow-k8/cpufreq looks wrong. > After looking closer at this, better would have been: > /sys/devices/system/cpu/boost_mode > if capable. Are you saying the boosting code should go somewhere else? We put it in powernow-k8 since it has mostly to do with Pstates and all... > > > Hmm, I'd prefer cleaner code (and only differing Intel/AMD once, either in > > > the kernel or in userspace), but the "you need kernel support for it and > > > cpufrequtils might run on older kernel" arguement is interesting. > > > Not sure what is more important. Need to think a bit more about this. > > > Comments are very welcome. > > > > Ok, look at it this way: On the one hand, you need to be able to toggle > > boosting without having to install a tool for that. On the other, it is > > also important that cpufrequtils runs on as many kernels as possible. So > > you want to implement the toggling in userspace too. And I don't see an > > issue with code duplication because you already have most of it - you > > only need to iterate over the num_online_cpus and toggle the bit on each > > MSR. 10 additional lines tops. > I thought a bit about this and I do not see a way to implement this in > userspace. The reason is CPU onlining/offlining. > If userspace could lock CPUs to not get offlined, then set cpb enable > or disable bits on all cores or break out if not all CPUs are online is > what you need. > But you cannot do: "lock CPUs to not get offlined" in userspace and if > you could you would certainly run into quite some other issues. I think you're referring to the maybe-possible case when cores disappear from under you while you're toggling boosting, right? Hmm, we could maybe do get/put_cpu() in <arch/x86/kernel/msr.c> to have it hotplug-safe to a certain degree but there might be cases where this might not fly... > So for now that param may get implemented through: > /sys/devices/system/cpu/cpu0/cpufreq/cpb > at some time, but there is no urgent need. On the other hand, having a single system-wide sysfs knob is simpler for userspace. Hmm, let me dream a bit more on this. However, if we do it this way, cpufreq will depend on a kernel version. Implementing boosting in it would be trivial, though :) Thanks. -- Regards/Gruss, Boris. Advanced Micro Devices GmbH Einsteinring 24, 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Gemeinde Aschheim, Landkreis Muenchen Registergericht Muenchen, HRB Nr. 43632 -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
