On Mon, Jun 29, 2015 at 10:32 PM, Andres Freund <andres@anarazel.de> wrote:
> On 2015-06-29 22:11:33 -0400, Robert Haas wrote:
>> On Mon, Jun 29, 2015 at 6:11 AM, Andres Freund <andres@anarazel.de> wrote:
>> > On 2015-06-29 00:42:53 -0400, Tom Lane wrote:
>> >> #define S_UNLOCK(lock) \
>> >> do { _Asm_sched_fence(); (*(lock)) = 0; } while (0)
>> >
>> > Robert, how did you choose that? Isn't _Asm_sched_fence just a compiler
>> > barrier? Shouldn't this be a _Asm_mf()?
>>
>> The point of the commit was to make spinlocks act as compiler barriers
>> as well as CPU barriers. So I was just looking to add a compiler
>> barrier to what was already there.
>
> You removed a volatile at the same time, and volatile on IA64 has
> acquire/release semantics.
Can you explain what you mean by volatile having acquire/release
semantics? I don't see how volatile can create a CPU barrier, but I'm
guessing that it somehow can and that you're about to enlighten me.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
