>-----Original Message----- >From: Pavel Machek [mailto:pavel@xxxxxx] >Sent: Friday, March 05, 2010 1:20 AM >To: Pallipadi, Venkatesh >Cc: Randy Dunlap; Ingo Molnar; H Peter Anvin; Thomas Gleixner; >Len Brown; Dave Jones; linux-kernel@xxxxxxxxxxxxxxx; >linux-acpi@xxxxxxxxxxxxxxx >Subject: Re: [patch 2/2] x86: Manage ENERGY_PERF_BIAS based on >cpufreq governor > >> On Wed, 2010-03-03 at 13:57 -0800, Pavel Machek wrote: >> > Hi! >> > >> > > index 8c666d8..4945add 100644 >> > > --- a/Documentation/kernel-parameters.txt >> > > +++ b/Documentation/kernel-parameters.txt >> > > @@ -749,6 +749,10 @@ and is between 256 and 4096 >characters. It is defined in the file >> > > Default value is 0. >> > > Value can be changed at runtime >via /selinux/enforce. >> > > >> > > + epb [X86] Control >IA32_ENERGY_PERF_BIAS setting >> > > + "disable" - Kernel will not >modify this MSR >> > > + <0..15> - Kernel will set this >MSR to i/p static value >> > > + >> > > >> > > >> > > Should be more like: >> > > >> > > epb= [X86] Control IA32_ENERGY_PERF_BIAS setting >> > > Format: { disable | <0...15> } >> > > "disable" - Kernel will not modify this MSR >> > > <0..15> - Kernel will set this MSR to >i/p static value >> > > >> > > >> > > But what is "i/p"? Use whatever word it should be, please. >> > > What do the values mean? >> > > And what does IA32 have to do with this? does it not >apply to x86_64? >> > >> > Exactly. This is end user documentation, it should not >even talk about >> > MSRs. Tell us what the setting does... >> >> The not so good part of this feature is that the setting >here is opaque. >> Software can set this based on its preference, for example 0 for >> performance 15 for power and 7 for balanced. Different CPUs >can use this >> information to do different optimizations or >power-performance tradeoffs >> in the hardware. The only thing that user knows here is that there is >> this dial with 16 possible values. I can remove the MSR name >here. But, >> I think that will end up confusing the end user on what this thing is >> and how it is related to all the other tunables we have in >the kernel. >> Having the MSR name gives a hint. > >You should say what the setting does; you can mention below what MSR >it corresponds to, but "Control IA32_ENERGY_PERF_BIAS setting" is not >suitable user documentation. > >> Also, the expectation here is that kernel will do the right thing by >> default. The option here is to the user who_knows_what_he_is_doing to >> override the kernel default. > >You did not give user enough information to do anything intelligent... I have rephrased it in the newer version sent yday with more info. >> > Also... does it make change to tweak the setting during >runtime? Maybe >> > different settings for AC and battery power? >> >> Yes. Matthew mentioned in other response aboue setting this based on >> freq. For the CPUs that support this feature currently, we don't see >> advantage in setting this feature at run time. > >If the feature is useless, then why set it at all? I just said changing it at run time doesn't give us benefits. Not that the feature is useless. Having the default value for the tunable in mid-range does increase energy-efficiency than the tunable being at performance level. Thanks, Venki-- 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
