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Subject[PATCH] ext4: Use trace condition for ext4_mballoc tracepoints
Doing an if statement to test some condition to know if we should
trigger a tracepoint is pointless when tracing is disabled. This just
adds overhead and wastes a branch prediction. This is why the
TRACE_EVENT_CONDITION() was created. It places the check inside the jump
label so that the branch does not happen unless tracing is enabled.

That is, instead of doing:

if (em)
trace_btrfs_get_extent(root, em);

Which is basically this:

if (em)
if (static_key(trace_btrfs_get_extent)) {

Using a TRACE_EVENT_CONDITION() we can just do:

trace_btrfs_get_extent(root, em);

And the condition trace event will do:

if (static_key(trace_btrfs_get_extent)) {
if (em) {

The static key is a non conditional jump (or nop) that is faster than
having to check if em is NULL or not.

Signed-off-by: Steven Rostedt <>

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