Re: [PATCH v5 06/11] RISC-V: Strengthen atomic stores

[Palmer Dabbelt]

On Fri, 28 Apr 2023 10:40:15 PDT (-0700), jeffreya...@gmail.com wrote:


On 4/27/23 10:22, Patrick O'Neill wrote:
This change makes atomic stores strictly stronger than table A.6 of the
ISA manual. This mapping makes the overall patchset compatible with
table A.7 as well.

2023-04-27 Patrick O'Neill <patr...@rivosinc.com>

        PR 89835
Should be "PR target/89835"


gcc/ChangeLog:

        * config/riscv/sync.md:
Needs some text here :-)


I'm not objecting to this patch, but I think we've got an option
question about whether or not this approach is too expensive for
existing or soon arriving implementations.

If the decision on that topic is to just pay the cost, then this patch
is fine.  If we decide to make compatibility optional to avoid the
additional cost, then this will need suitable adjustments.

IMO the only hardware that's going to be here by gcc-14 and to have 
enough concurrency for these to matter is the Ventana stuff.  I think 
you're the only one who can figure out if these are slow, at least until 
that stuff is availiable outside the lab.

So are they too slow for you?


Jeff