Skip to content

Commit

Permalink
tracing: Improve "if" macro code generation
Browse files Browse the repository at this point in the history
With CONFIG_PROFILE_ALL_BRANCHES=y, the "if" macro converts the
conditional to an array index.  This can cause GCC to create horrible
code.  When there are nested ifs, the generated code uses register
values to encode branching decisions.

Make it easier for GCC to optimize by keeping the conditional as a
conditional rather than converting it to an integer.  This shrinks the
generated code quite a bit, and also makes the code sane enough for
objtool to understand.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: brgerst@gmail.com
Cc: catalin.marinas@arm.com
Cc: dvlasenk@redhat.com
Cc: dvyukov@google.com
Cc: hpa@zytor.com
Cc: james.morse@arm.com
Cc: julien.thierry@arm.com
Cc: luto@amacapital.net
Cc: luto@kernel.org
Cc: rostedt@goodmis.org
Cc: valentin.schneider@arm.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190307174802.46fmpysxyo35hh43@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
  • Loading branch information
Josh Poimboeuf authored and Ingo Molnar committed Apr 3, 2019
1 parent 6690e86 commit 37686b1
Showing 1 changed file with 1 addition and 1 deletion.
2 changes: 1 addition & 1 deletion include/linux/compiler.h
Original file line number Diff line number Diff line change
Expand Up @@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
.line = __LINE__, \
}; \
______r = !!(cond); \
______f.miss_hit[______r]++; \
______r ? ______f.miss_hit[1]++ : ______f.miss_hit[0]++;\
______r; \
}))
#endif /* CONFIG_PROFILE_ALL_BRANCHES */
Expand Down

0 comments on commit 37686b1

Please sign in to comment.