timer stats: speedups
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>
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Linus Torvalds

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c1a834dc70
@@ -126,7 +126,10 @@ config TIMER_STATS
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reprogrammed. The statistics can be read from /proc/timer_stats.
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The statistics collection is started by writing 1 to /proc/timer_stats,
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writing 0 stops it. This feature is useful to collect information
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about timer usage patterns in kernel and userspace.
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about timer usage patterns in kernel and userspace. This feature
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is lightweight if enabled in the kernel config but not activated
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(it defaults to deactivated on bootup and will only be activated
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if some application like powertop activates it explicitly).
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config DEBUG_SLAB
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bool "Debug slab memory allocations"
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