File:  [NetBSD Developer Wiki] / wikisrc / projects / project / tickless.mdwn
Revision 1.2: download - view: text, annotated - select for diffs
Mon Feb 22 20:52:49 2016 UTC (4 years ago) by riastradh
Branches: MAIN
CVS tags: HEAD
Fix subject/verb plural agreement.

[[!template id=project

title="Tickless NetBSD with high-resolution timers"

contact="""
[tech-kern](mailto:tech-kern@NetBSD.org)
"""

mentors="""
[Taylor R Campbell](mailto:riastradh@NetBSD.org)
"""

category="kernel"
difficulty="hard"
duration="2-3 months"

description="""
NetBSD configures a timer device to deliver a periodic timer interrupt,
 usually every 10 ms, in order to count time, wake threads that are
 sleeping, etc.
This made sense when timer devices were expensive to program and CPUs
 ran at MHz.
But today, CPUs run at GHz; timers on modern x86, arm, mips,
 etc. hardware are cheap to reprogram; programs expect greater than
 10 ms resolution for sleep times; and mandatory periodic activity on
 idle machines wastes power.

There are three main miletones to this project:

1. Design a machine-independent high-resolution timer API, implement it
 on a couple machines, and develop tests to confirm that it works, in
 order to enable high-resolution sleeps.

2. Convert all the functions of the periodic 10 ms timer, `hardclock',
 to schedule activity only when needed.

3. Convert the various software subsystems that rely on periodic timer
 interrupts every tick, or every second, via
 [callouts](http://netbsd.gw.com/cgi-bin/man-cgi?callout++NetBSD-current),
 either to avoid periodic work altogether, or to batch it up only when
 the machine is about to go idle, in order to reduce the number of
 wakeups and thereby reduce power consumption.
"""
]]

[[!tag gsoc]]

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