x86: Manage ENERGY_PERF_BIAS based on cpufreq governor
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From: Matthew Garrett on 3 Mar 2010 11:50 Have you done any measurements with this bit being set dynamically by ondemand depending on the target frequency? -- Matthew Garrett | mjg59(a)srcf.ucam.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Pavel Machek on 3 Mar 2010 17:00 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... Also... does it make change to tweak the setting during runtime? Maybe different settings for AC and battery power? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Pavel Machek on 5 Mar 2010 04:30 > 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... > > 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? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Pallipadi, Venkatesh on 5 Mar 2010 09:40 >-----Original Message----- >From: Pavel Machek [mailto:pavel(a)ucw.cz] >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(a)vger.kernel.org; >linux-acpi(a)vger.kernel.org >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-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Matthew Garrett on 5 Mar 2010 16:00
On Fri, Mar 05, 2010 at 09:40:29PM +0100, Pavel Machek wrote: > That can be only true if it does not give benefits period... AC and > battery power are quite different scenarios. No, they're not. -- Matthew Garrett | mjg59(a)srcf.ucam.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |