[RFC/RFT] calloutng

[Alexander Motin]

Hi.

Here is one more version. Unless something new will be found/reported 
this may be the last one, because me and Davide are quite satisfied with 
the results. If everything will be fine, I think we could commit it to 
HEAD closer to the end of the week:
http://people.freebsd.org/~mav/calloutng_12_16.patch

Changes in this version:
  -- Removed couple of redundant variables in callout implementation, 
that reduced sizeof(struct callout) by two pointers and simplified some 
internal code.
  -- syscons driver was made to schedule only 1-2 callouts per second 
instead of 20-30 before when console is in graphical mode and there are 
few other things to do. Now my laptop has only about 30 interrupts per 
second total during idle periods with X running.
  -- i8254 eventtimer driver was optimized to work faster in disabled by 
default one-shot mode.
  -- Few kernel functions were added to make KPIs more complete.
  -- Man pages were updated.
  -- Some style fixes were made.

On 15.12.2012 18:55, Alexander Motin wrote:
> I'm sorry to interrupt review, but as usual good ideas came during the
> final testing, causing another round. :)  Here is updated patch for
> HEAD, that includes several new changes:
> http://people.freebsd.org/~mav/calloutng_12_15.patch
>
> The new changes are:
>   -- Precision and event aggregation code was reworked. Instead of
> previous -prec/+prec representation, precision is now single-sided --
> -0/+prec. It allowed to significantly improve precision on long time
> intervals for APIs which imply that event should not happen before the
> specified time. Depending on CPU activity, mistake for long time
> intervals now will never be more then 1-500ms, even if specified
> precision allows more.
>   -- Some minor optimizations were made to reduce callout overhead and
> latency by 1.5-2us. Now on Core2Duo amd64 system with LAPIC eventtimer
> and TSC timecounter usleep(1) call from user-level executes in just
> 5-6us, instead of 7-8us before. Now it can do 180K cycles per second on
> single CPU with only partial CPU load.
>   -- Number of kernel subsystems (dcons, syscons, yarrow, led, atkbd,
> setrlimit) were modified to reduce number of interrupts, also with event
> aggregation by explicit specification of the acceptable events
> precision. Now my Core2Duo test system has only 30 interrupts per second
> in idle. If not remaining syscons events, it could easily be 15. My
> IvyBridge ultrabook first time in its history shown 5.5 hours of battery
> time with full screen brightness and 10 hours with lid closed.
>   -- Some kernel functions were added to make KPIs more complete.
>
> I've successfully tested this patch on amd64 and arm.
>


-- 
Alexander Motin