Messages in this thread | | | Date | Thu, 9 May 2019 13:45:31 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 02/25] tracing: Improve "if" macro code generation |
| |
On Thu, May 09, 2019 at 02:29:02PM -0400, Steven Rostedt wrote: > On Thu, 9 May 2019 09:51:59 -0700 > Linus Torvalds <torvalds@linux-foundation.org> wrote: > > > On Thu, May 9, 2019 at 6:01 AM Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > > This patch works. Can I get your Signed-off-by for it? > > > > Yes. Please write some kind of comprehensible commit log for it, but > > How's this: > > "Peter Zijlstra noticed that with CONFIG_PROFILE_ALL_BRANCHES, 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. > > Josh Poimboeuf found that replacing the define "if" macro from using > the condition as an array index and incrementing the branch statics > with an if statement itself, reduced the asm complexity and shrinks the > generated code quite a bit. > > But this can be simplified even further by replacing the internal if > statement with a ternary operator. > > Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Reported-by: Josh Poimboeuf <jpoimboe@redhat.com>
Actually, my original fix already went in:
37686b1353cf ("tracing: Improve "if" macro code generation")
But it introduced a regression:
https://lkml.kernel.org/r/201905040509.iqQ2CrOU%lkp@intel.com
which Linus' patch fixes for some reason.
-- Josh
| |