Re: Misaligned BufferDescriptors causing major performance problems on AMD

On Thu, Apr 17, 2014 at 11:23:24AM +0200, Andres Freund wrote:
> On 2014-04-16 19:18:02 -0400, Bruce Momjian wrote:
> > On Thu, Feb 6, 2014 at 09:40:32AM +0100, Andres Freund wrote:
> > > On 2014-02-05 12:36:42 -0500, Robert Haas wrote:
> > > > >> It may well be that your proposal is spot on. But I'd like to see some
> > > > >> data-structure-by-data-structure measurements, rather than assuming that
> > > > >> alignment must be a good thing.
> > > > >
> > > > > I am fine with just aligning BufferDescriptors properly. That has
> > > > > clearly shown massive improvements.
> > > >
> > > > I thought your previous idea of increasing BUFFERALIGN to 64 bytes had
> > > > a lot to recommend it.
> > >
> > > Good.
> > >
> > > I wonder if we shouldn't move that bit of logic:
> > > if (size >= BUFSIZ)
> > > newStart = BUFFERALIGN(newStart);
> > > out of ShmemAlloc() and instead have a ShmemAllocAligned() and
> > > ShmemInitStructAligned() that does it. So we can sensibly can control it
> > > per struct.
> > >
> > > > But that doesn't mean it doesn't need testing.
> > >
> > > I feel the need here, to say that I never said it doesn't need testing
> > > and never thought it didn't...
> >
> > Where are we on this?
>
> It needs somebody with time to evaluate possible performance regressions
> - I personally won't have time to look into this in detail before pgcon.

Again, has anyone made any headway on this? Is it a TODO item?

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Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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