Dave Hansen <dave.han...@linux.intel.com> wrote: > 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.
I agree that with the whole Meltdown/Spectre entry-cost it might not even be measurable, at least on small ( < 2 sockets) machines. But I do not think it worth profiling. Basically, AFAIK, all the data structures that are used for inter-processor communication by the kernel are aligned, and this is an exception.
