Re: Misaligned BufferDescriptors causing major performance problems on AMD

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?

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