Hi,
first of all thanks to everybody for all this comments!
On 10/26/2012 05:56 AM, Peter Zijlstra wrote:
On Fri, 2012-10-26 at 12:44 +0200, Peter Zijlstra wrote:
We can still have the user space interface handing in the information
in nsec resolution, but it's reasonable to scale it down to something
useful. Just shift the incoming information right by 10, so you're in
the 1us resolution for all the internal math and all your limitation
problems are gone. A shift by ten for converting back and forth to
nsecs is not a real performance issue.
I'm fine with that.. all I wanted was to not have the undefined overflow
we initially had.
Note that we still need the constraint checking with this, although with
both values shifted right 10 bits the range is now much bigger and
shouldn't be a practical limit anymore.
I'll try to recap what seems to me you agreed and what will be the
changes for the next iteration.
- remove first two patches (u128 math) [and keep them in a safe place
just in case following constraints will annoy future generation users
:P]
- scale down (right by 10) incoming parameters as to do internal
math with ~1us resolution (and scale up outgoing params)
- insert new constraints on -dl entities parameters:
o since we have - dl_period >= dl_deadline >= dl_runtime - the
only constraint we have to add for the overflow problem should
be dl_period * dl_runtime < U64_MAX
o to rule out problems with <= 1000ns parameters just force the user
to pass > 1000ns parameters (in the end its our real resolution)
- WARN_ONCE() in proper places
- properly document all this (comments and Documentation)
What you think?
Thanks a lot and Regards,
- Juri
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