Re: [PATCH v6 0/4] riscv: tlb flush improvements

[Palmer Dabbelt]

On Mon, 30 Oct 2023 07:01:48 PDT (-0700), nadav.amit@xxxxxxxxx wrote:
> > On Oct 30, 2023, at 3:30 PM, Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> wrote:
> >
> > +			on_each_cpu_mask(cmask,
> > +					 __ipi_flush_tlb_range_asid,
> > +					 &ftd, 1);
>
> Unrelated, but having fed

Do you mean `ftd`?

If so I'm not all that convinced that's a problem: sure it's 4x`long`, 
so we pass it on the stack instead of registers, but otherwise we'd need 
another `on_each_cpu_mask()` callback to shim stuff through via 
registers.

> on the stack might cause it to be unaligned to
> the cacheline, which in x86 we have seen introduces some overhead.

We have 128-bit stack alignment on RISC-V, so the elements are at least 
aligned.  Since they're just being loaded up as scalars for the next 
function call I'm not sure the alignment is all that exciting here.

> Actually, it is best not to put it on the stack, if possible to reduce
> cache traffic.

Sorry if I'm just missing something, but I'm not convinced this is a 
measurable performance problem.