Hi Jason,
Quoting "Jason A. Donenfeld" <Jason@xxxxxxxxx>:
On Fri, Oct 4, 2019 at 4:44 PM Ard Biesheuvel
<ard.biesheuvel@xxxxxxxxxx> wrote:
The round count is passed via the fifth function parameter, so it is
already on the stack. Reloading it for every block doesn't sound like
a huge deal to me.
Please benchmark it to indicate that, if it really isn't a big deal. I
recall finding that memory accesses on common mips32r2 commodity
router hardware was extremely inefficient. The whole thing is designed
to minimize memory accesses, which are the primary bottleneck on that
platform.
I also think it isn't a big deal, but I shall benchmark it this weekend.
If I am correct a memory write will first put in cache. So if you read
it again and it is in cache it is very fast. 1 or 2 clockcycles.
Also the value isn't used directly after it is read.
So cpu don't have to stall on this read.
Greats,
René
Seems like this thing might be best deferred for after this all lands.
IOW, let's get this in with the 20 round original now, and later you
can submit a change for the 12 round and René and I can spend time
dusting off our test rigs and seeing which strategy works best. I very
nearly tossed out a bunch of old router hardware last night when
cleaning up. Glad I saved it!
