| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Reduce ProcArrayLock contention |
| Date: | 2015-08-04 15:51:20 |
| Message-ID: | 20150804155120.GA32119@awork2.anarazel.de |
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| Lists: | pgsql-hackers |
On 2015-08-04 11:43:45 -0400, Robert Haas wrote:
> On Tue, Aug 4, 2015 at 11:33 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > Actually by far not all system calls are full barriers?
>
> How do we know which ones are and which ones are not?
Good question. Reading the source code of all implementations I suppose
:(
E.g. gettimeofday()/clock_gettime(), getpid() on linux aren't
barriers.
> I can't believe PGSemaphoreUnlock isn't a barrier. That would be cruel.
Yea, I think that's a pretty safe bet. I mean even if you'd implement it
locklessly in the kernel, that'd still employ significant enough
barriers/atomic ops itself.
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