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timer stats: speedups

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Make timer-stats have almost zero overhead when enabled in the config but
not used.  (this way distros can enable it more easily)

Also update the documentation about overhead of timer_stats - it was
written for the first version which had a global lock and a linear list
walk based lookup ;-)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ingo Molnar
2007-06-01 00:47:16 -07:00
committed by Linus Torvalds
parent 9fcc15ec3c
commit c1a834dc70
3 changed files with 14 additions and 5 deletions
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7
Documentation/hrtimer/timer_stats.txt
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@@ -2,9 +2,10 @@ timer_stats - timer usage statistics
------------------------------------
timer_stats is a debugging facility to make the timer (ab)usage in a Linux
system visible to kernel and userspace developers. It is not intended for
production usage as it adds significant overhead to the (hr)timer code and the
(hr)timer data structures.
system visible to kernel and userspace developers. If enabled in the config
but not used it has almost zero runtime overhead, and a relatively small
data structure overhead. Even if collection is enabled runtime all the
locking is per-CPU and lookup is hashed.
timer_stats should be used by kernel and userspace developers to verify that
their code does not make unduly use of timers. This helps to avoid unnecessary