Horton

Re: [HACKERS] Deadlock in XLogInsert at AIX

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Noah Misch <noah@leadboat.com>
Cc: Michael Paquier <michael.paquier@gmail.com>, Andres Freund <andres@anarazel.de>, Heikki Linnakangas <hlinnaka@iki.fi>, Konstantin Knizhnik <k.knizhnik@postgrespro.ru>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Bernd Helmle <mailings@oopsware.de>
Date: 2019-08-31T18:27:55Z
Lists: pgsql-hackers 
Noah Misch <noah@leadboat.com> writes:
> Done.  fetch-add-variable-test-v1.patch just adds tests for non-constant
> addends and 16-bit edge cases.  Today's implementation handles those,
> PostgreSQL doesn't use them, and I might easily have broken them.
> fetch-add-xlc-asm-v1.patch moves xlc builds from the __fetch_and_add()
> intrinsic to inline asm.  fetch-add-gcc-xlc-unify-v1.patch moves fetch_add to
> inline asm for all other ppc compilers.  gcc-7.2.0 generates equivalent code
> before and after.  I plan to keep the third patch HEAD-only, back-patching the
> other two.  I tested with xlc v12 and v13.

Hm, no objection to the first two patches, but I don't understand
why the third patch goes to so much effort just to use "addi" rather
than (one assumes) "li" then "add"?  It doesn't seem likely that
that's buying much.

			regards, tom lane

Commits

  1. For all ppc compilers, implement compare_exchange and fetch_add with asm.

  2. For PowerPC instruction "addi", use constraint "b".

  3. For all ppc compilers, implement pg_atomic_fetch_add_ with inline asm.

  4. Replace xlc __fetch_and_add() with inline asm.

  5. Test pg_atomic_fetch_add_ with variable addend and 16-bit edge cases.