On Tue, 27 May 2014, Daniel Lezcano wrote:
> On 05/27/2014 12:19 AM, Nicolas Pitre wrote:
> > "Power" is a very bad term in the scheduler context. There are so many
> > meanings that can be attached to it. And with the upcoming "power
> > aware" scheduler work, confusion is sure to happen.
> >
> > The definition of "power" is typically the rate at which work is performed,
> > energy is converted or electric energy is transferred. The notion of
> > "compute capacity" is rather at odds with "power" to the point many
> > comments in the code have to make it explicit that "capacity" is the
> > actual intended meaning.
> >
> > So let's make it clear what we man by using "capacity" in place of "power"
> > directly in the code. That will make the introduction of actual "power
> > consumption" concepts much clearer later on.
> >
> > This is based on the latest tip tree to apply correctly on top of existing
> > scheduler changes already queued there.
> >
> > Changes from v1:
> >
> > - capa_factor and SCHED_CAPA_* changed to be spelled "capacity" in full
> > to save peterz some Chupacabra nightmares
> >
> > - some minor corrections in commit logs
> >
> > - rebased on latest tip tree
> >
> >
> > arch/arm/kernel/topology.c | 54 +++----
> > include/linux/sched.h | 8 +-
> > kernel/sched/core.c | 87 ++++++-----
> > kernel/sched/fair.c | 323 ++++++++++++++++++++-------------------
> > kernel/sched/sched.h | 18 +--
> > 5 files changed, 246 insertions(+), 244 deletions(-)
>
> Hi Nico,
>
> it is a good initiative to replace the 'power' word by another to prevent
> confusion for future code. Personally I have a preference to 'strength'
> instead of 'capacity', in case that matter.
Proper usage does matter:
Strength could mean many things. Among them:
Physical ability
* Physical strength, as in people or animals
As an abstract or psychological trait
* Virtue and moral uprightness
* Courage or fortitude in the face of moral or social pressure
* Persuasiveness of an argument
* The exercise of willpower
Physics
* Strength of materials, ability to withstand an applied stress
without failure
+ Compressive strength, capacity to withstand axially directed
pushing forces
+ Tensile strength, maximum stress while being stretched or
pulled before necking
+ Shear strength, the ability to withstand shearing
* Strength (explosive), the ability of an explosive to move
surrounding material
* Field strength, the magnitude of a field's vector
* Signal strength, the magnitude of an electric field at a
reference point
I have difficulty referring to "CPU strength" without still be confused
about what exactly this would mean. None of the above definitions would
provide a sufficiently close analogy to be applied without ambiguity.
On the other hand, the definition for capacity is much narrower:
1.
a. The ability to receive, hold, or absorb.
b. Abbr. c. A measure of this ability; volume.
2. The maximum amount that can be contained: a trunk filled to capacity.
3.
a. Ability to perform or produce; capability.
b. The maximum or optimum amount that can be produced: factories
operating below capacity.
Etc.
Here the analogy with "CPU capacity" or "compute capacity" is clear and
natural for what we are applying this term to.
Nicolas
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
