Horton

Re: better atomics - v0.6

Heikki Linnakangas <hlinnakangas@vmware.com>

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From: Heikki Linnakangas <hlinnakangas@vmware.com>
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: 2014-09-24T15:55:51Z
Lists: pgsql-hackers 
On 09/24/2014 03:37 PM, Andres Freund wrote:
>>> > >+/*
>>> > >+ * pg_fetch_add_until_u32 - saturated addition to variable
>>> > >+ *
>>> > >+ * Returns the the value of ptr after the arithmetic operation.
>>> > >+ *
>>> > >+ * Full barrier semantics.
>>> > >+ */
>>> > >+STATIC_IF_INLINE uint32
>>> > >+pg_atomic_fetch_add_until_u32(volatile pg_atomic_uint32 *ptr, int32 add_,
>>> > >+							  uint32 until)
>>> > >+{
>>> > >+	CHECK_POINTER_ALIGNMENT(ptr, 4);
>>> > >+	return pg_atomic_fetch_add_until_u32_impl(ptr, add_, until);
>>> > >+}
>>> > >+
>> >
>> >This was a surprise to me, I don't recall discussion of an "fetch-add-until"
>> >operation, and hadn't actually ever heard of it before.
> It was included from the first version on, and I'd mentioned it a couple
> times.

There doesn't seem to be any hardware implementations of that in the 
patch. Is there any architecture that has an instruction or compiler 
intrinsic for that?

- Heikki

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