| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(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: | 2015-01-01 19:49:06 |
| Message-ID: | CA+Tgmoa0MZJz7dwrV=L+2Y7XRUbNuwr681+ue8DmAY1vvSXP+A@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Jan 1, 2015 at 11:59 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> The problem is that just aligning the main allocation to some boundary
> doesn't mean the hot part of the allocation is properly aligned. shmem.c
> in fact can't really do much about that - so fully moving the
> responsibility seems more likely to ensure that future code thinks about
> alignment.
That's true, but if you don't align the beginnings of the allocations,
then it's a lot more complicated for the code to properly align stuff
within the allocation. It's got to insert a variable amount of
padding based on the alignment it happens to get.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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