| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(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 20:04:48 |
| Message-ID: | 6EDE41C6-BFB2-44CC-9FE0-0CDFBE455308@2ndquadrant.com |
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| Lists: | pgsql-hackers |
On January 1, 2015 8:49:06 PM CET, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>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.
Hm? Allocate +PG_CACHELINE_SIZE and do var = CACHELINEALIGN(var).
--
Please excuse brevity and formatting - I am writing this on my mobile phone.
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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