Re: [PATCH] x86: Align TLB invalidation info

[Dave Hansen]

On 01/31/2018 12:11 PM, Nadav Amit wrote:
> The TLB invalidation info is allocated on the stack, which might cause
> it to be unaligned. Since this information may be transferred to
> different cores for TLB shootdown, this might result in an additional
> cache-line bouncing between the cores.
> 
> GCC provides a way to deal with it by using
> __builtin_alloca_with_align(). Use it to avoid the bouncing cache lines.

It doesn't really *bounce*, though, does it?  I don't see any writes on
the remote side.  The remote use seems entirely read-only.

You also don't have to exhaustively test this, but I'd love to see at
least a sanity check with a microbenchmark (or something) that, yes,
this does help *something*.  Maybe it makes the remote
flush_tlb_func_common() run faster because it's pulling in fewer lines,
or maybe you can even detect fewer misses in there.