AutoFDO Optimizations For The GCC Compiler

[phoronix]

Phoronix: AutoFDO Optimizations For The GCC Compiler

A patch has emerged that provides "AutoFDO" support for the GCC compiler for automated feedback-directed optimizations...

http://www.phoronix.com/vr.php?view=MTE5NTc

[WorBlux]

What exactly is the difference between PGO (profile guided optimization) and FDO?

[XorEaxEax]

What exactly is the difference between PGO (profile guided optimization) and FDO?

The name, some compilers refer to it as profile-guided-optimization, others call it feedback-driven-optimization, the technique is the same.

One thing Micheal wrote was '-So this implementation is also faster than the traditional Feedback Directed Optimization (FDO) support currently found in GCC', now from the author's mail: -'This can bring 50% to 110% of the speedup derived by traditional instrumentation based FDO. (Average is between 70% to 80% for many CPU intensive applications).'

I grok this as it generally gives 70-80% of the performance normal FDO (PGO) gives and ranges from faster (110%) or slower (%50), so saying it is faster than traditional PGO is a bit optimistic as it seems to general case is 70-80% of the speed traditional PGO gives.

That said, it would be great to have a automated way to use PGO and thus avoid the hassle of either manual profile-gathering or writing an application-specific automation in order to utilize this optimization. Here's hoping it makes it into trunk, certainly interested in trying this.

[curaga]

The way I read it, this still requires the representative runtime to be actually useful.

So it's merely a question of setting up perf infrastructure vs building a PGO-instrumented binary. Given I don't have the perf things set up, I would rate the PGO approach as easier