Horton

Re: [HACKERS] Deadlock in XLogInsert at AIX

Michael Paquier <michael.paquier@gmail.com>

View thread View on postgr.es
From: Michael Paquier <michael.paquier@gmail.com>
To: Noah Misch <noah@leadboat.com>
Cc: 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: 2018-01-20T23:16:30Z
Lists: pgsql-hackers 
On Wed, Jan 17, 2018 at 12:36:31AM -0800, Noah Misch wrote:
> For me, verifiability is the crucial benefit of inline asm.  Anyone with an
> architecture manual can thoroughly review an inline asm implementation.  Given
> intrinsics and __xlc_ver__ conditionals, the same level of review requires
> access to every xlc version.

Okay.

> The most recent patch version is Returned with Feedback.  As a matter of
> procedure, I discourage creating commitfest entries as a tool to solicit new
> patch versions.  If I were the author of a RwF patch, I would dislike finding
> a commitfest entry that I did not create with myself listed as author.

Per my understanding, this is a bug, and we don't want to lose track of
them.

> If you do choose to proceed, the entry should be Waiting on Author.

Right.

> Note that fixing this bug is just the start of accepting XLC 13.1 as a
> compiler of PostgreSQL.  If we get a buildfarm member with a few dozen clean
> runs (blocked by, at a minimum, fixing this and the inlining bug), we'll have
> something.  Until then, support for XLC 13.1 is an anti-feature.

Per my understanding of this thread, this is a bug. My point is that the
documentation states that AIX is supported from 4.3.3 to 6.1, however
there are no restrictions related to the compiler, hence I would have
thought that the docs imply XLC 13.1 as a supported compiler. And IBM
states that XLC 13.1 is supported from AIX 6.1:
https://www-01.ibm.com/support/docview.wss?uid=swg21326972

True that the docs tell as well to look at the buildfarm animals, which
don't use XLC 13.1 if you don't look at them closely. Perhaps an
explicit mention of the compiler compatibilities in the docs would help
making the support range clear to anybody then. I would expect more
people to look at the docs than the buildfarm internal contents.
--
Michael

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.