Object file section efficiency

[Valdis.Kletnieks at vt.edu]

On Mon, 24 Feb 2014 12:44:33 -0800, Matt Davis said:

> Are there any memory efficiencies with how the kernel loads the .data
> vs the .rodata sections into memory?  Will the information stored in
> .rodata have better cache performance than that stored in .data?

Yes/no/maybe.  It's mostly going to depend on whether there's any *other*
hot data in the same cache line.  There's been a number of patches that
re-organize various structs that are larger than a cache line so that all
the hot data is in the same line.  There's also been patches to *split*
data across 2 cache lines to avoid ping-ponging (where CPU 1 is beating up
on variable A, and CPU 2 is beating up on not-very-related variable B, and
they just keep shooting down the cache line).
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