Kernel Timer Systems - Revision history

Cschalle: Add category

2011-10-27T22:38:11Z

Add category

WillNewton at 15:25, 24 November 2008

2008-11-24T15:25:03Z

WillNewton: /* Timer information */

2008-11-24T15:23:26Z

‎Timer information

WillNewton: /* Dynamic ticks */

2008-11-24T15:22:21Z

‎Dynamic ticks

Tim Bird: /* /proc/timer_stats */

2007-10-29T18:39:59Z

‎/proc/timer_stats

Tim Bird: /* /proc/timer_list */

2007-10-29T18:38:21Z

‎/proc/timer_list

Tim Bird at 18:26, 29 October 2007

2007-10-29T18:26:38Z

Tim Bird: /* Testing */ add poor-man's powertop command

2007-10-23T01:00:20Z

‎Testing: add poor-man's powertop command

Tim Bird: /* Testing */

2007-10-23T00:31:24Z

‎Testing

Tim Bird: /* Testing */

2007-10-23T00:31:01Z

‎Testing

← Older revision		Revision as of 22:38, 27 October 2011
Line 149:		Line 149:
	- high res timer for periodic absolute wakeup (wake up every 10 ms, whether last one was late or nt		- high res timer for periodic absolute wakeup (wake up every 10 ms, whether last one was late or nt
	- high res timer for periodic relative wakeup (wake up 10 ms from now)		- high res timer for periodic relative wakeup (wake up 10 ms from now)
		+
		+	[[Category:Kernel]]

← Older revision		Revision as of 15:25, 24 November 2008
Line 1:		Line 1:
−	~~This page has links to information about the (relatively) new timer systems for the Linux kernel.~~
−	~~The current linux kernel received a major enhancement to it's timer system (as of about 2.6.21),~~
−	~~which solved a number of problems.~~
−
−	~~A good article on the subject is at at lwn.net: [http://lwn.net/Articles/223185/ Clockevents and dyntick]~~
−
−	~~-------------------~~
−
	== Timer Wheel, Jiffies and HZ (or, the way it was) ==		== Timer Wheel, Jiffies and HZ (or, the way it was) ==
	The original kernel timer system (called the "timer wheel) was based on		The original kernel timer system (called the "timer wheel) was based on

@@ Line 39: / Line 39: @@
 == Timer information ==
 There are two /proc files that are very useful for
 === /proc/timer_list ===
 /proc/timer_list has information about the currently configured clocks and timers on the system.
 This is useful for debugging the current status of the timer system (especially while you are developing
@@ Line 60: / Line 63: @@
 === /proc/timer_stats ===
-/proc/timer_stats is a file in the /proc psuedo file system which allows you to see information
 about the routines that are requesting timers of the Linux kernel.  By cat'ing this file,
 you can see which routines are using lots of timers, and how frequently they are requesting them.

@@ Line 86: / Line 86: @@
 == Dynamic ticks ==
-The configuration option is: CONFIG_NO_HZ
+Tickless kernel, dynamic ticks or NO_HZ is a config option that enables a kernel to run without a regular timer tick. The timer tick is a timer interrupt that is usually generated HZ times per second, with the value of HZ being set at compile time and varying between around 100 to 1500. Running without a timer tick means the kernel does less work when idle and can potentially save power because it does not have to wake up regularly just to service the timer. The configuration option is CONFIG_NO_HZ and is set by Tickless System (Dynamic Ticks), on the Kernel Features configuration menu.
-Prompt is: Tickless System (Dynamic Ticks), on the Kernel Features configuration menu.
+* See the [http://lwn.net/Articles/223185/ Clockevents and dyntick] LNW.net article
 === Testing ===
-You can look at the timer interrupts and compare to jiffies:
+To tell if dynamic ticks is supported in your kernel you can:
-   cat /proc/interrupts | grep -i time
+   # dmesg | grep -i nohz
-   sleep 10
+   Switched to NOHz mode on CPU #0
-  cat /proc/interrupts | grep -i time
-You can use powertop on embedded processors, but in order to get a clean display
+Powertop is a tool that parses the /proc/timer_stats output and gives a picture of what is causing wakeups on your system. Minimizing these wakeups should allow you to decrease power consumption in your device. Powertop was originally written for the x86 architecture but also works for embedded processors. However, in order to get a clean display from it, you will need an ncurses lib with wide character support.
-from it, you need an ncurses lib with wide-char support. (From Kevin Hilman, Oct 2007)
 Here's a poor-man's version of powertop:
-*  watch "cat /proc/timer_stats | sort -nr | head -n 20"
+  # watch "cat /proc/timer_stats | sort -nr | head -n 20"
 == timer API ==

@@ Line 77: / Line 77: @@
 To stop collecting stats, do "echo 0 >/proc/timer_stats"
-Then, cat /proc/timer_stats, and it gives and average events/sec at
+You can dump the statistics either while the collection system
 the end as well so you get a rough idea of system activity.

@@ Line 44: / Line 44: @@
 This is useful for debugging the current status of the timer system (especially while you are developing
 clockevent and clocksource support for your platform.)
 You can tell if high resolution is configured for you machine by looking at a few different things:
@@ Line 55: / Line 53: @@
 Also for standard resolution, the Clock Event Device will have an event handler of "tick_handle_periodic".
-For high resolution, the resolution of the clock will listed as 1 nanosecond
+For high resolution, the resolution of the clock will be listed as 1 nanosecond
 (which is ridiculous, but serves as an indicator of essentially arbitrary precision.)
 Also, the Clock Event Device will have an event handler of "hrtimer_interrupt".
+----
+[need more info here - and this should probably be written up and put in Documentation/filesystems/proc.txt]
-−
-−
-−
-−
 === /proc/timer_stats ===

← Older revision		Revision as of 00:31, 23 October 2007
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	/proc/timer_stats fields (for version 0.1 of the format) are:		/proc/timer_stats fields (for version 0.1 of the format) are:
−	<count>, <pid> <command> <start_func> (<expire_func>)	+	<count>, <pid> <command> <start_func> (<expire_func>)