Horton

Re: JIT compiling with LLVM v12

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Andres Freund <andres@anarazel.de>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, pgsql-hackers@postgresql.org
Date: 2018-08-22T06:20:21Z
Lists: pgsql-hackers 
On Wed, Mar 28, 2018 at 02:27:51PM -0700, Andres Freund wrote:
> For now LLVM is enabled by default when compiled --with-llvm. I'm mildly
> inclined to leave it like that until shortly before the release, and
> then disable it by default (i.e. change the default of jit=off). But I
> think we can make that decision based on experience during the testing
> window. I'm opening an open items entry for that.

I'll vote for jit=on and letting any bugs shake out earlier, but it's not a
strong preference.

I see jit slows the regression tests considerably:

# x86_64, non-assert, w/o llvm
$ for n in 1 2 3; do env time make -C src/bin/pg_upgrade check; done 2>&1 | grep elapsed
7.64user 4.24system 0:36.40elapsed 32%CPU (0avgtext+0avgdata 36712maxresident)k
8.09user 4.50system 0:37.71elapsed 33%CPU (0avgtext+0avgdata 36712maxresident)k
7.53user 4.18system 0:36.54elapsed 32%CPU (0avgtext+0avgdata 36712maxresident)k

# x86_64, non-assert, w/  llvm trunk
$ for n in 1 2 3; do env time make -C src/bin/pg_upgrade check; done 2>&1 | grep elapsed
9.58user 5.79system 0:49.61elapsed 30%CPU (0avgtext+0avgdata 36712maxresident)k
9.47user 5.92system 0:47.84elapsed 32%CPU (0avgtext+0avgdata 36712maxresident)k
9.09user 5.51system 0:47.94elapsed 30%CPU (0avgtext+0avgdata 36712maxresident)k

# mips32el, assert, w/o llvm (buildfarm member topminnow) [1]
28min install-check-*
35min check-pg_upgrade

# mips32el, assert, w/  llvm 6.0.1 [1]
 63min install-check-*
166min check-pg_upgrade

Regardless of the choice of jit={on|off} default, these numbers tell me that
some or all of jit_*_cost defaults are too low.


[1] The mips32el runs used "nice -+20" and ran on a shared machine.  I include
them to show the trend, but exact figures may be non-reproducible.

Commits

  1. Improve JIT docs.

  2. Add documentation for the JIT feature.

  3. Add EXPLAIN support for JIT.

  4. Add inlining support to LLVM JIT provider.

  5. JIT tuple deforming in LLVM JIT provider.

  6. Add FIELDNO_* macro designating offset into structs required for JIT.

  7. Add expression compilation support to LLVM JIT provider.

  8. Expand list of synchronized types and functions in LLVM JIT provider.

  9. Add helpers for emitting LLVM IR.

  10. Basic planner and executor integration for JIT.

  11. Debugging and profiling support for LLVM JIT provider.

  12. Support for optimizing and emitting code in LLVM JIT provider.

  13. Add file containing extensions of the LLVM C API.

  14. Basic JIT provider and error handling infrastructure.

  15. Add configure infrastructure (--with-llvm) to enable LLVM support.

  16. Add C++ support to configure.

  17. Add PGAC_PROG_VARCC_VARFLAGS_OPT autoconf macro.

  18. Fix VM buffer pin management in heap_lock_updated_tuple_rec().

  19. Allow tupleslots to have a fixed tupledesc, use in executor nodes.

  20. Expression evaluation based aggregate transition invocation.

  21. Perform slot validity checks in a separate pass over expression.

  22. Rely on executor utils to build targetlist for DML RETURNING.

  23. Refer to OS X as "macOS", except for the port name which is still "darwin".