| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Greg Stark <stark(at)mit(dot)edu>, Peter Geoghegan <pg(at)heroku(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Misaligned BufferDescriptors causing major performance problems on AMD |
| Date: | 2015-01-28 18:52:30 |
| Message-ID: | 5011.1422471150@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On 2015-01-28 13:38:51 -0500, Tom Lane wrote:
>> #define BUFFERDESC_PADDED_SIZE (SIZEOF_VOID_P == 8 ? 64 : 32)
> Hm, did you intentionally put a 32in there or was that just the logical
> continuation of 64? Because there's no way it'll ever fit into 32 bytes
> in the near future. That's why I had put the sizeof(BufferDesc)
> there. We could just make it 1 as well, to indicate that we don't want
> any padding...
Yeah, 1 would be fine too. Maybe better to call it BUFFERDESC_MIN_SIZE,
because as this stands it's enforcing a min size not exact size. (I'm
not going to whinge about that aspect of it; the main point here is to
put in the union and fix the ensuing notational fallout. We can worry
about exactly what size to pad to as a separate discussion.)
regards, tom lane
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