Messages in this thread | | | Date | Tue, 19 Mar 2019 11:11:23 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 02/25] tracing: Improve "if" macro code generation |
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On Mon, Mar 18, 2019 at 06:37:20PM -0500, Josh Poimboeuf wrote: > On Mon, Mar 18, 2019 at 04:38:42PM +0100, Peter Zijlstra wrote: > > 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. > > > > 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. > > > > Cc: rostedt@goodmis.org > > Cc: valentin.schneider@arm.com > > Cc: luto@amacapital.net > > Cc: brgerst@gmail.com > > Cc: catalin.marinas@arm.com > > Cc: mingo@kernel.org > > Cc: dvlasenk@redhat.com > > Cc: will.deacon@arm.com > > Cc: julien.thierry@arm.com > > Cc: torvalds@linux-foundation.org > > Cc: dvyukov@google.com > > Cc: bp@alien8.de > > Cc: tglx@linutronix.de > > Cc: james.morse@arm.com > > Cc: luto@kernel.org > > Cc: hpa@zytor.com > > Reported-by: Peter Zijlstra <peterz@infradead.org> > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > Link: https://lkml.kernel.org/r/20190307174802.46fmpysxyo35hh43@treble > > Missing "From" me.
Right, sorry, quilt eats that and I sometimes forget to fix up :/
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