From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Sokolov Yura <funny(dot)falcon(at)postgrespro(dot)ru>, 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 16:09:11 |
Message-ID: | CA+TgmobhVejJDdwUtOp+oSnd+oM68qZLUt0ArB_xKES2TMWeWQ@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Wed, Sep 6, 2017 at 12:01 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> This seems like a pretty sound argument to me. I think Tom's probably
>> right that the changes in generic-gcc.h are the important ones, but
>> I'm not sure that's an argument against patching generics.h. Given
>> that pg_atomic_compare_exchange_u32_impl is defined to update *old
>> there seems to be no reason to call pg_atomic_read_u32_impl every time
>> through the loop.
>
> Probably not. I'm not quite 100% convinced of that, because of my
> observation that gcc is capable of generating different and better
> code for some of these primitives if it can prove that the return
> value is not needed. It's not clear that that could apply in any
> of these uses of pg_atomic_compare_exchange_u32_impl, though.
> In any case, by my own argument, it shouldn't matter, because if
> any of these are really performance-critical then we should be
> looking for better ways.
It's not a question of whether the return value is used, but of
whether the updated value of *old is used.
Unless I'm confused.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2017-09-06 16:16:12 | Re: [COMMITTERS] pgsql: Add psql variables showing server version and psql version. |
Previous Message | Tom Lane | 2017-09-06 16:01:24 | Re: Fix performance of generic atomics |