Re: [PATCH 02/25] tracing: Improve "if" macro code generation

[Randy Dunlap]

On 5/9/19 11:47 AM, Josh Poimboeuf wrote:
> On Thu, May 09, 2019 at 01:45:31PM -0500, Josh Poimboeuf wrote:
>> 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@xxxxxxxxxxxxxxxxxxxx> wrote:
>>>
>>>> On Thu, May 9, 2019 at 6:01 AM Steven Rostedt <rostedt@xxxxxxxxxxx> 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@xxxxxxxxxxxxx>
>>> Reported-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
>>
>> 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@xxxxxxxxx
>>
>> which Linus' patch fixes for some reason.
> 
> /me curses URL encoding
> 
> https://lkml.kernel.org/r/201905040509.iqQ2CrOU%25lkp@xxxxxxxxx
> 

Still fails for me.

-- 
~Randy