forked from Minki/linux
4cd8587ce8
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 <rostedt@goodmis.org>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
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| acpi | ||
| asm-generic | ||
| clocksource | ||
| crypto | ||
| drm | ||
| dt-bindings | ||
| keys | ||
| kvm | ||
| linux | ||
| math-emu | ||
| media | ||
| memory | ||
| misc | ||
| net | ||
| pcmcia | ||
| ras | ||
| rdma | ||
| rxrpc | ||
| scsi | ||
| sound | ||
| target | ||
| trace | ||
| uapi | ||
| video | ||
| xen | ||
| Kbuild | ||