Re: An unlikely() experiment

On 30 October 2017 at 22:34, Andres Freund <andres(at)anarazel(dot)de> wrote:
> Hi,
>
> On 2015-12-20 02:49:13 +1300, David Rowley wrote:
>> Alternatively, if there was some way to mark the path as cold from within
>> the path, rather than from the if() condition before the path, then we
>> could perhaps do something in the elog() macro instead. I just couldn't
>> figure out a way to do this.
>
> I just was thinking about this, and it turns out that
> __attribute__((cold)) does what we need here. We could just mark
> elog_start() and errstart() as cold, and afaict that should do the
> trick.

I had actually been thinking about this again today. I had previously
not thought __attribute__((cold)) would be a good idea since if we
mark elog_start() with that, then code paths with elog(NOTICE) and
elog(LOG) not to mention DEBUG would be marked as cold. Today I was
thinking, to get around that issue, we might be able to generate
another thin wrapper around elog_start() and mark that as
__attribute__((cold)) and fudge the macro a bit to call that function
instead if it can detect a compile time const level >= ERROR. I've not
looked at the code again to remind myself if that would be possible.

--
David Rowley http://www.2ndQuadrant.com/
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