[libre-riscv-dev] GPU design

lkcl lkcl at libre-riscv.org
Wed Dec 5 09:33:21 GMT 2018

On Wed, Dec 5, 2018 at 9:23 AM Jacob Lifshay <programmerjake at gmail.com> wrote:
> having a scoreboard doesn't mean you have to have imprecise exceptions, you
> could have a scoreboard + reorder buffer,

 ahh ok.  hm let me think that one through.

on first impressions, i _think_ it basically means that it's the same
as the tomasulo+rob, except with the reservation stations removed, the
scoreboard is now the central bottleneck _and_ there is one extra
clock cycle (at least) where results which formerly went directly from
outputs over the CDB into multiple locations must now go to the
register file...

 ... or, not the register file but the register _rename_file, instead.

in other words the reg-rename file is very similar to the reservation stations.

> or you could have the scoreboard
> not execute instructions until all prior instructions are known to not trap.

 which means having to assess them all and special-case them.  LD/ST
being the main ones.

> If we ended up with imprecise exceptions, I'd be very tempted to just build
> a barrel processor instead.

 yehyeh.  well, let's keep exploring.


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