Horton

Re: xlc atomics

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Noah Misch <noah@leadboat.com>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>, Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Peter Geoghegan <pg@heroku.com>, Ants Aasma <ants@cybertec.at>
Date: 2016-02-15T17:33:42Z
Lists: pgsql-hackers 
On 2016-02-15 12:11:29 -0500, Noah Misch wrote:
> These suggested OidGenLock wasn't doing its job.  I've seen similar symptoms
> around WALInsertLocks with "IBM XL C/C++ for Linux, V13.1.2 (5725-C73,
> 5765-J08)" for ppc64le.  The problem is generic-xlc.h
> pg_atomic_compare_exchange_u32_impl() issuing __isync() before
> __compare_and_swap().  __isync() shall follow __compare_and_swap(); see our
> own s_lock.h, its references, and other projects' usage:

Ugh. You're right! It's about not moving code before the stwcx...

Do you want to add the new test (no objection, curious), or is that more
for testing?

Greetings,

Andres

Commits

  1. Avoid the use of a separate spinlock to protect a LWLock's wait queue.

  2. Improve LWLock scalability.

  3. Reduce the number of semaphores used under --disable-spinlocks.

  4. Alter the configure script to fail immediately if the C compiler does not