| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, 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: | 2015-01-27 01:04:07 |
| Message-ID: | 20150127010407.GF4655@awork2.anarazel.de |
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| Thread: | |
| Lists: | pgsql-hackers |
On 2015-01-26 19:58:25 -0500, Bruce Momjian wrote:
> On Tue, Jan 27, 2015 at 01:43:41AM +0100, Andres Freund wrote:
> > master + 32align.patch:
> > -c max_connections=400
> > tps = 183791.872359 (high run vs. run variability)
> > -c max_connections=401
> > tps = 185494.98244 (high run vs. run variability)
> >
> > master + 64align.patch:
> > -c max_connections=400
> > tps = 489257.195570
> > -c max_connections=401
> > tps = 490496.520632
> >
> > Pretty much as expected, rigth?
>
> Yes, I am convinced. Let's work on a patch now.
Since I can reproduce some minor (1-3%) performance *regressions* at low
client counts when aligning every shmem allocation, I'm inclined to just
add special case code to BufferShmemSize()/InitBufferPool() to align
descriptors to PG_CACHE_LINE_SIZE. That's really unlikely to regress
anythign as it basically can't be a bad idea to align buffer
descriptors.
Contrary opinions? Robert?
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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