Linked by Eugenia Loli-Queru on Thu 26th Apr 2007 06:36 UTC, submitted by RJop
Linux Kernel 2.6.21 has been announced. Linus writes: "So the big change during 2.6.21 is all the timer changes to support a tickless system (and even with ticks, more varied time sources). Thanks (when it no longer broke for lots of people ;) go to Thomas Gleixner and Ingo Molnar and a cadre of testers and coders." More info here and here.
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Member since:2006-01-16
Well some part is missing. There are processes that want to be woken up after X milliseconds.
So the system has also to make sure to wake up at the next of these events.
A reasonable solution would be to disable the timer interrupt only of no process waits for a timing event, but if so, change the interrupt's frequency according to it.
It is explained here: http://kernelnewbies.org/Linux_2_6_21#head-8547911895fda9cdff32a947...
Edited 2007-04-26 17:14
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Member since:
2005-12-06
As far as I understand it (but please bear in mind I'm no expert), tickless means that the kernel will not necessarily wake up periodically anymore.
Originally, a timer was programmed to generate an interrupt ("timer tick") a fixed number of times per second, usually in the range of 100-1000 Hz. That also meant the processor would possibly wake from sleep that many times per second, causing unnecessary power consumption on a lightly loaded system.
A tickless system might disable the timer interrupt altogether when entering an idle state, so it will only wake up when an I/O device demands the attention of the kernel. Of course it would be re-enabled again as soon as multiple processes are competing for processor resources.
If anyone has corrections to the information stated above, please don't hesitate to post them. I'm curious about the exact implications as well.