Re: Align large shared memory allocations

Manfred Spraul <manfred(at)colorfullife(dot)com> writes:
> Attached is a patch that aligns large shared memory allocations beyond
> MAXIMUM_ALIGNOF. The reason for this is that Intel's cpus have a fast
> path for bulk memory copies that only works with aligned addresses.

This patch is missing a demonstration that it's actually worth anything.
What kind of performance gain do you get?

> One problem is the "32" - it's arbitrary, it probably belongs into an
> arch dependant header file. But where?

We don't really have arch-dependent header files. What I'd be inclined
to do is "#define ALIGNOF_BUFFER 32" in pg_config_manual.h, then
#define BUFFERALIGN(LEN) to parallel the other TYPEALIGN macros in c.h,
and finally use that in the ShmemAlloc code.

regards, tom lane