Re: better atomics - v0.6

Oskari Saarenmaa <os@ohmu.fi>

From: Oskari Saarenmaa <os@ohmu.fi>
To: Andres Freund <andres@2ndquadrant.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Peter Geoghegan <pg@heroku.com>, Pg Hackers <pgsql-hackers@postgresql.org>, Ants Aasma <ants@cybertec.at>
Date: 2014-09-23T21:27:25Z
Lists: pgsql-hackers

Attachments

23.09.2014, 15:18, Andres Freund kirjoitti:
> On 2014-09-23 13:50:28 +0300, Oskari Saarenmaa wrote:
>> 23.09.2014, 00:01, Andres Freund kirjoitti:
>>> The patches:
>>> 0001: The actual atomics API
>>
>> I tried building PG on Solaris 10/Sparc using GCC 4.9.0 (buildfarm animal
>> dingo) with this patch but regression tests failed due to:
>
> Btw, if you could try sun studio it'd be great. I wrote the support for
> it blindly, and I'd be surprised if I got it right on the first try.

I just installed Solaris Studio 12.3 and tried compiling this:

"../../../../src/include/port/atomics/generic-sunpro.h", line 54: return 
value type mismatch
"../../../../src/include/port/atomics/generic-sunpro.h", line 77: return 
value type mismatch
"../../../../src/include/port/atomics/generic-sunpro.h", line 79: 
#if-less #endif
"../../../../src/include/port/atomics/generic-sunpro.h", line 81: 
#if-less #endif

atomic_add_64 and atomic_add_32 don't return anything (the 
atomic_add_*_nv variants return the new value) and there were a few 
extra #endifs.  Regression tests pass after applying the attached patch 
which defines PG_HAS_ATOMIC_ADD_FETCH_U32.

There doesn't seem to be a fallback for defining pg_atomic_fetch_add 
based on pg_atomic_add_fetch so pg_atomic_add_fetch now gets implemented 
using pg_atomic_compare_exchange.

Also, it's not possible to compile PG with FORCE_ATOMICS_BASED_SPINLOCKS 
with these patches:

"../../../../src/include/storage/s_lock.h", line 868: #error: PostgreSQL 
does not have native spinlock support on this platform....

atomics/generic.h would implement atomic flags using operations exposed 
by atomics/generic-sunpro.h, but atomics/fallback.h is included before 
it and it defines functions for flag operations which s_lock.h doesn't 
want to use.

/ Oskari

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