Priorities regarding base system work....

[Jim Gettys]

I think I'd like to spark a discussion of priorities regarding base
system work.  Right now, I think we're in a bit of a random walk.  And
note that lower priority work does not make it less important: just that
it could be done later. This is not saying that no lower priority work
gets done while the higher priority work is underway; people, skills and
interests are not fully interchangeable between projects.

Please push back if you think I'm all wet.

*The* low hanging fruit that can save the most energy is suspend/resume.
If the machine is *correctly* powered off, it isn't consuming power.

Zeroth priority: Through all of this *must* be measurement: we cannot
afford to put resources in places that don't pay off.  So let's not
presume we know where the problems are: let's take measurements that
show us *where* the problems are.  Both how much power is used by what
parts of the boards, and what the system is doing.

First priority: bring up and testing of hardware.  If we don't have some
function of the hardware working, we need to.  While doing the driver
work, we should be aware of, and take care around power management and
in particularly suspend/resume.  We are mostly but not entirely through
this process, and won't be until the CaFe drivers are fully debugged and
integrated.  Furthermore, we have to verify the hardware all works
correctly, and all power domains can be properly controlled,  *and* that
any buses are properly disabled (which can cause parasitic power
consumption).  Machines can't be manufactured until we believe the
hardware works correctly, and we understand failures.

Second priority: fast suspend/resume.  This can save more power than all
the rest of the kernel and application work we do put together, for most
workloads.  CPU's not running consume no power ;-).  As part of this,
though, we have to verify carefully that the drivers are in fact
powering off all the devices and buses properly.

Third priority: Elapsed time performance of applications.  Items like
the systemtap results on the amazing number of files that python opens
and reads affect both the interactive feel, and also how much work the
CPU is doing as a result, will also save power.

Fourth priority: Background wakeups of the processor, tickless
operation, etc, unless we find, by measurement, terrible hotspots that
need fixing.

Comments,
                                   Regards,
                                 - Jim

-- 
Jim Gettys
One Laptop Per Child