| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Sokolov Yura <funny(dot)falcon(at)postgrespro(dot)ru>, Robert Haas <robertmhaas(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Fix performance of generic atomics |
| Date: | 2017-09-06 19:12:13 |
| Message-ID: | 32578.1504725133@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2017-09-06 14:31:26 -0400, Tom Lane wrote:
>> However, if that's the reasoning, why don't we make all of these
>> use simple reads? It seems unlikely that a locked read is free.
> We don't really use locked reads? All the _atomic_ wrapper forces is an
> actual read from memory rather than a register.
It looks to me like two of the three implementations promise no such
thing. Even if they somehow do, it hardly matters given that the cmpxchg
loop would be self-correcting. Mostly, though, I'm looking at the
fallback pg_atomic_read_u64_impl implementation (with a CAS), which
seems far more expensive than can be justified for this.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Tom Lane | 2017-09-06 19:18:27 | Re: why not parallel seq scan for slow functions |
| Previous Message | Robert Haas | 2017-09-06 19:11:08 | Re: why not parallel seq scan for slow functions |