Re: use of LIKELY() and UNLIKELY() branch predictors

On Tue, Jan 29, 2013 at 01:58:03PM -0500, bulk88 wrote:
> Dave Mitchell wrote:
> >Perl defines the LIKELY() and UNLIKELY() macros, which (under gcc)
> >tell the compiler whether a particular expression is likely to be true or
> >not. This allows you to re-write something like
> 
> Why do it by hand, rather than use
> http://en.wikipedia.org/wiki/Profile-guided_optimization with a real
> work load (what is a real workload?)?

Well, there's the rub. perl doesn't have a standard "workload" suite. The
test suite is specifically not useful for this sort of thing, since it
likes testing edge cases and exercising all those branches that would
normally not be taken.

And one person's "standard" workload is another person's atypical one.
Realistically, any profiling should be done by the end user on perl
running their own applications to build a perl optimised for their own
workload.

-- 
You live and learn (although usually you just live).

• use of LIKELY() and UNLIKELY() branch predictors by Dave Mitchell
• Re: use of LIKELY() and UNLIKELY() branch predictors by bulk88
• Re: use of LIKELY() and UNLIKELY() branch predictors by Dave Mitchell
• Re: use of LIKELY() and UNLIKELY() branch predictors by Tim Bunce
• Re: use of LIKELY() and UNLIKELY() branch predictors by Dave Mitchell
• Re: use of LIKELY() and UNLIKELY() branch predictors by Steffen Mueller
• Re: use of LIKELY() and UNLIKELY() branch predictors by bulk88
• Re: use of LIKELY() and UNLIKELY() branch predictors by Zefram
• Re: use of LIKELY() and UNLIKELY() branch predictors by Steffen Mueller
• Re: use of LIKELY() and UNLIKELY() branch predictors by Nicholas Clark
• Re: use of LIKELY() and UNLIKELY() branch predictors by Zefram
• Re: use of LIKELY() and UNLIKELY() branch predictors by David Cantrell
• Re: use of LIKELY() and UNLIKELY() branch predictors by Tim Bunce
• Re: use of LIKELY() and UNLIKELY() branch predictors by demerphq
• Re: use of LIKELY() and UNLIKELY() branch predictors by Zefram
• Re: use of LIKELY() and UNLIKELY() branch predictors by hv
• Re: use of LIKELY() and UNLIKELY() branch predictors by Zefram
• Re: use of LIKELY() and UNLIKELY() branch predictors by Tim Bunce
• Re: use of LIKELY() and UNLIKELY() branch predictors by Dave Mitchell
• Re: use of LIKELY() and UNLIKELY() branch predictors by Nicholas Clark