Re: [RFC/RFT] calloutng

Hi.

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