On Fri, 27 Jun 2008 17:13:24 +0100
Richard Hughes <hughsient@gmail.com> wrote:

> At the moment we set:
>
> # CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
> CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE=y
> # CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND is not set
> # CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE is not set
> CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
> CONFIG_CPU_FREQ_GOV_POWERSAVE=m
> CONFIG_CPU_FREQ_GOV_USERSPACE=y
> CONFIG_CPU_FREQ_GOV_ONDEMAND=m
> CONFIG_CPU_FREQ_GOV_CONSERVATIVE=m
>
> This is not ideal from a power-saving point of view.
>
> In an ideal world we would:
>
> * remove CONFIG_CPU_FREQ_GOV_CONSERVATIVE -- ondemand does a better
> job on all workloads
> * remove CONFIG_CPU_FREQ_GOV_USERSPACE -- we have nothing in
> userspace that needs this sort of control, and if we did, the latency
> would be horrible
> * remove CONFIG_CPU_FREQ_GOV_POWERSAVE -- ondemand automatically
> throttles down to lowest, and is just a hardcoded state
> * compile into the kernel CONFIG_CPU_FREQ_GOV_ONDEMAND -- we really
> want to be running this on all systems that support it
> * set ONDEMAND or PERFORMANCE to default as USERSPACE is just
> changed to something else by cpuspeed. You really don't want to be
> using USERSPACE at all.
>
> Matthew Garrett and I are working on a latency profile for power
> management, and having all these modules potentially loaded is bad.
>
> Comments?
>

I totally agree with your suggestions.



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Richard Hughes wrote:
> In an ideal world we would:

> * compile into the kernel CONFIG_CPU_FREQ_GOV_ONDEMAND -- we really
> want to be running this on all systems that support it
> * set ONDEMAND or PERFORMANCE to default as USERSPACE is just changed
> to something else by cpuspeed. You really don't want to be using
> USERSPACE at all.

How can an administrator set a known constant frequency, so that the CPU
might be able to deliver the same amount of work per unit time,
over a span of half an hour? Some performance measurement and tuning
is much simpler when this is so.

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On Fri, Jun 27, 2008 at 6:13 PM, Richard Hughes <hughsient@gmail.com> wrote:
> You really don't want to be using
> USERSPACE at all.

seems like cpufreq-applet uses it....

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On Fri, Jun 27, 2008 at 05:13:24PM +0100, Richard Hughes wrote:
> At the moment we set:
>
> # CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
> CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE=y
> # CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND is not set
> # CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE is not set
> CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
> CONFIG_CPU_FREQ_GOV_POWERSAVE=m
> CONFIG_CPU_FREQ_GOV_USERSPACE=y
> CONFIG_CPU_FREQ_GOV_ONDEMAND=m
> CONFIG_CPU_FREQ_GOV_CONSERVATIVE=m
>
> This is not ideal from a power-saving point of view.
>
> In an ideal world we would:
>
> * remove CONFIG_CPU_FREQ_GOV_CONSERVATIVE -- ondemand does a better job
> on all workloads
> * remove CONFIG_CPU_FREQ_GOV_USERSPACE -- we have nothing in userspace
> that needs this sort of control, and if we did, the latency would be
> horrible

needed for the cpuspeed governor

> * remove CONFIG_CPU_FREQ_GOV_POWERSAVE -- ondemand automatically
> throttles down to lowest, and is just a hardcoded state
> * compile into the kernel CONFIG_CPU_FREQ_GOV_ONDEMAND -- we really
> want to be running this on all systems that support it
> * set ONDEMAND or PERFORMANCE to default as USERSPACE is just changed
> to something else by cpuspeed. You really don't want to be using
> USERSPACE at all.

Not all CPUs are capable of running ondemand because of the latency they
incur during transitions.

> Matthew Garrett and I are working on a latency profile for power
> management, and having all these modules potentially loaded is bad.

I don't follow this. Can you show whatever numbers you have that you're
basing this on ?

Dave

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On Fri, 2008-06-27 at 21:16 +0200, drago01 wrote:
> On Fri, Jun 27, 2008 at 6:13 PM, Richard Hughes <hughsient@gmail.com>
> wrote:
> > You really don't want to be using
> > USERSPACE at all.
>
> seems like cpufreq-applet uses it....

Sure, it shouldn't. If you're using userspace for thermal or latency
reasons, then a setuid applet is totally the wrong way to achieve both
of these :-)

Maybe we can just use these as loadable modules (i.e. not built default)
rather than built-in and loaded by default.

DaveJ, do these suggestions seem acceptable?

Richard.


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