Re: JIT compiling with LLVM v9.0

Hi,

On 2018-01-29 15:45:56 +0300, Konstantin Knizhnik wrote:
> On 26.01.2018 22:38, Andres Freund wrote:
> > And without it perf is not able to unwind stack trace for generated
> > > code.
> > You can work around that by using --call-graph lbr with a sufficiently
> > new perf. That'll not know function names et al, but at least the parent
> > will be associated correctly.
>
> With --call-graph lbr result is ... slightly different (see attached
> profile) but still there is "unknown" bar.

Right. All that allows is to attribute the cost below the parent in the
perf report --children case. For it to be attributed to proper symbols
you need my llvm patch to support pef.

> Actually I am trying to find answer for the question why your version of JIT
> provides ~2 times speedup at Q1, while ISPRAS version (https://www.pgcon.org/2017/schedule/attachments/467_PGCon%202017-05-26%2015-00%20ISPRAS%20Dynamic%20Compilation%20of%20SQL%20Queries%20in%20PostgreSQL%20Using%20LLVM%20JIT.pdf)
> speedup Q1 is 5.5x times.
> May be it is because them are using double type to calculate aggregates
> while as far as I understand you are using standard Postgres aggregate
> functions?
> Or may be because ISPRAS version is not checking for NULL values...

All of those together, yes. And added that I'm aiming to work
incrementally towards core inclusions, rather than getting the best
results. There's a *lot* that can be done to improve the generated code
- after e.g. hacking together an improvement to the argument passing (by
allocating isnull / nargs / arg[], argnull[] as a separate on-stack from
FunctionCallInfoData), I get another 1.8x. Eliminating redundant float
overflow checks gives another 1.2x. And so on.

Greetings,

Andres Freund