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authorSteven Rostedt (Red Hat) <srostedt@redhat.com>2013-03-05 10:25:16 -0500
committerSteven Rostedt <rostedt@goodmis.org>2013-03-07 10:31:22 -0500
commitd8741e2e88ac9a458765a0c7b4e6542d7c038334 (patch)
treeef455e17665c8a956c618e2860715e21f799ec44 /kernel/notifier.c
parenta335358f52aec4397594043ac799d15f92e728dd (diff)
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tracing: Add help of snapshot feature when snapshot is empty
When cat'ing the snapshot file, instead of showing an empty trace header like the trace file does, show how to use the snapshot feature. Also, this is a good place to show if the snapshot has been allocated or not. Users may want to "pre allocate" the snapshot to have a fast "swap" of the current buffer. Otherwise, a swap would be slow and might fail as it would need to allocate the snapshot buffer, and that might fail under tight memory constraints. Here's what it looked like before: # tracer: nop # # entries-in-buffer/entries-written: 0/0 #P:4 # # _-----=> irqs-off # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / delay # TASK-PID CPU# |||| TIMESTAMP FUNCTION # | | | |||| | | Here's what it looks like now: # tracer: nop # # # * Snapshot is freed * # # Snapshot commands: # echo 0 > snapshot : Clears and frees snapshot buffer # echo 1 > snapshot : Allocates snapshot buffer, if not already allocated. # Takes a snapshot of the main buffer. # echo 2 > snapshot : Clears snapshot buffer (but does not allocate) # (Doesn't have to be '2' works with any number that # is not a '0' or '1') Acked-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/notifier.c')
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